A safety warning for electric under sink water heater.

I'm just in from repairing a boiler in a Creche and while I was there I checked their under sinkwater heaters, both of the heaters were fitted in a manor that could allow the children using the Creche to be hurt.

Undersink water heaters have the very real potential to damage people and property, they should be fitted in a way that takes the potential risks into account so as to leave a safe installation for those using the heater.

Undersink water heaters are commonly fitted in schools and creches in places very close to the children using them, rarely are the heaters fitted with the full understanding of the risks posed to the children.

These heaters are often passed as being safe

I'd like to ask fellow tradesmen who find themselves in a position to check these heaters to do so taking into account:positioning, blending valves, plastic pipe, expansion, safety valves and safe termination.

Thanks, Gary.

Calahonda52

It would be useful to pen a few words on what the issues are and what folk, such a teachers or carers should be aware of.

I understand and appreciate the sentiment in the post but I don't think enumerating and elucidating the risks etc should be confined to those lucky enough to card a RGII or RECI card.
Children's safety is all our concerns.
First off are these gas or elec or nuke powered

Calahonda52

Calahonda52 wrote: »

It would be useful to pen a few words on what the issues are and what folk, such a teachers or carers should be aware of.

I understand and appreciate the sentiment in the post but I don't think enumerating and elucidating the risks etc should be confined to those lucky enough to card a RGII or RECI card.
Children's safety is all our concerns.
First off are these gas or elec or nuke powered

The clue is in the title;)

Firstly I don't understand the big words so go easy with me, it's nothing to do with RGI or RECI, it's basic plumbing, pressurised water when heated will expand(common cause for these heaters bursting).

From my experiences I find it very difficult to get anyone to take ownership for protential safety issues with unvented electric undersink water heater as they choose not to believe anything bad will happen.

I often get a lot of grief for highlighting unvented safety issues.

Anybody who wishes to check their heater should be asking themselves if it burst where does the water go?

If the safety valve lifts where does the water go?

If plastic pipe is fitted where will the water go if the plastic pipe melts from the heat?

Is the water at the tap thermostatically controlled?

Is there a fused spur within easy reach of the heater.

The water in these heaters can at times reach over 80c in normal operation so it's important to see how close these skin removing tempertures get to the kiddies.

Download the manufactures instructions for further information.

UK water regs are used by insurance companies to decide if a heater is fitted properly in the event of a claim, so I'd advise anyone fitting one to know what their responsibility are.

Billy Bunting

I think the sentiment was aimed at those who would have an understanding of the appliance, I would doubt very much that teachers or carers or indeed most without the "card" would have an idea of the difference between a blending valve and a safety valve let alone if they have been installed correctly.

John T Carroll

gary71 wrote: »

I'm just in from repairing a boiler in a Creche and while I was there I checked their under sinkwater heaters, both of the heaters were fitted in a manor that could allow the children using the Creche to be hurt.

Undersink water heaters have the very real potential to damage people and property, they should be fitted in a way that takes the potential risks into account so as to leave a safe installation for those using the heater.

Undersink water heaters are commonly fitted in schools and creches in places very close to the children using them, rarely are the heaters fitted with the full understanding of the risks posed to the children.

These heaters are often passed as being safe

I'd like to ask fellow tradesmen who find themselves in a position to check these heaters to do so taking into account:positioning, blending valves, plastic pipe, expansion, safety valves and safe termination.

Thanks, Gary.

I had an Attic conversion carried out around 12 years ago, this was done by a very well established firm who specialise in this sort of work, they employed a separate electrician and plumber to carry out the necessary other works which included a "Velo Doccia" unvented electric hot water heater. The whole job seemed to be very well done.
I went to retrieve something from one of the crawl/storage spaces today and had a quick look at this heater and this is what I've found. The 1/2 ins qualpex seemed to be connected to the heater via a non return valve, the hot water outlet has a 2.5 meter run to the toilet hot tap. I isolated the water and electrical supply and disconnected the piping and found that it is indeed a NR valve fitted so I decided to carry out a few tests, I left the supply line disconnected and reinstated the electrical power and switched on the unit with the hot tap shut and very shortly afterwards water started to drip from the NR valve which (fortunately) is leaking. I then reconnected the piping and ran water through the unit until cool. I then isolated the water, removed the inlet line and capped the NR valve, I then opened the hot tap and switched on the heater and measured the expanded water until the heater cut out at 60C. I measured this at 90CC (0.09 Litre), this would seem correct by calculation as the heater is around 6 Ltrs and a 1.53% expansion (from 15c to 60C) gives 90CC. Now a 2.5 meter length of 1/2 ins qualpex is around 11.3 mm ID and I reckon this would hold about 250CC of water so it appears that a 90CC expansion was supposed to be accommodated by 250CC of pipework. I cant understand why this setup didn't at the very least blow some gasket or at the very worst cause far more damage especially when new and with a presumably tight NR valve. I have decommissioned the unit both electrically and hydraulically until I read up on the regs etc. I have attached pics of the NR valve, is it just possible that this was supplied with the hot water heater??, if it was it seems utterly crazy, I wouldn't have thought that an experienced plumber would have gone away and bought one of those but would have just plumbed it as is? I didn't remove the NR valve to have a good luck at it but I'm sure someone here will have some idea, is it possibly some form of combined NR/PRV.

John T Carroll

John T Carroll wrote: »

I had an Attic conversion carried out around 12 years ago, this was done by a very well established firm who specialise in this sort of work, they employed a separate electrician and plumber to carry out the necessary other works which included a "Velo Doccia" unvented electric hot water heater. The whole job seemed to be very well done.
I went to retrieve something from one of the crawl/storage spaces today and had a quick look at this heater and this is what I've found. The 1/2 ins qualpex seemed to be connected to the heater via a non return valve, the hot water outlet has a 2.5 meter run to the toilet hot tap. I isolated the water and electrical supply and disconnected the piping and found that it is indeed a NR valve fitted so I decided to carry out a few tests, I left the supply line disconnected and reinstated the electrical power and switched on the unit with the hot tap shut and very shortly afterwards water started to drip from the NR valve which (fortunately) is leaking. I then reconnected the piping and ran water through the unit until cool. I then isolated the water, removed the inlet line and capped the NR valve, I then opened the hot tap and switched on the heater and measured the expanded water until the heater cut out at 60C. I measured this at 90CC (0.09 Litre), this would seem correct by calculation as the heater is around 6 Ltrs and a 1.53% expansion (from 15c to 60C) gives 90CC. Now a 2.5 meter length of 1/2 ins qualpex is around 11.3 mm ID and I reckon this would hold about 250CC of water so it appears that a 90CC expansion was supposed to be accommodated by 250CC of pipework. I cant understand why this setup didn't at the very least blow some gasket or at the very worst cause far more damage especially when new and with a presumably tight NR valve. I have decommissioned the unit both electrically and hydraulically until I read up on the regs etc. I have attached pics of the NR valve, is it just possible that this was supplied with the hot water heater??, if it was it seems utterly crazy, I wouldn't have thought that an experienced plumber would have gone away and bought one of those but would have just plumbed it as is? I didn't remove the NR valve to have a good luck at it but I'm sure someone here will have some idea, is it possibly some form of combined NR/PRV.

The risk of the heater leaking/bursting is directly related to the incoming pressure, I find anything over 1 3/4 bar is more likly to have issues.

Firstly there is no regs and yours is a very very common installation that has at times caused 10s of thousands € worth of damage after the heaters burst.

The valve in your pic is usually rated at 8-9 bar and is a europeian valve and the one most commonly supplied/fitted, this is made more frightening when you look at plastic pipes reduced ability to deal with pressure as the heat increases leading to burst plastic pipes.

For your installation I'd advise fitting (towards the heater from the mains isolation valve) a pressure reducing valve if the water is over 3 1/2bar, a check valve/non-return valve, a 6 bar safety valve with a 1/2inch outlet so you can pipe the safety valve to terminate in a safe place with a tundish that doesn't allow water to leak if the valve opens and a expansion vessel to take up all expansion.

For the outlet I'm not a fan of plastic pipe and I like blending valves to protect users from potentially scalding themselves.

Joe1919

I had a flood in a house lately caused by the expansion pressure blowing the pipe off the top of the heater with an Ariston undersink heater. The unit in the photo is a combined one way valve and pressure release valve and there is a problem when these are fitted on the heaters when no allowance is made for water expansion.(e.g. expansion vessel)
I was not happy with the way it was fitted and made some changes. The heater was moved to a built in wardrobe and is now is fed from a separate low pressure supply from the storage tank and the non-return element of the valve is not used. The heater feeds two wash hand basins and a kitchen sink and is now ventilated.I used copper pipes to connect to heaters but plastic on the runs to basins from the 't'.
There is a good flow to taps despite the lower pressure and these heaters are very efficient. Its a pity about they way the are fitted.

Joe1919

Joe1919 wrote: »

I had a flood in a house lately caused by the expansion pressure blowing the pipe off the top of the heater with an Ariston undersink heater. The unit in the photo is a combined one way valve and pressure release valve and there is a problem when these are fitted on the heaters when no allowance is made for water expansion.(e.g. expansion vessel)
I was not happy with the way it was fitted and made some changes. The heater was moved to a built in wardrobe and is now is fed from a separate low pressure supply from the storage tank and the non-return element of the valve is not used. The heater feeds two wash hand basins and a kitchen sink and is now ventilated.I used copper pipes to connect to heaters but plastic on the runs to basins from the 't'.
There is a good flow to taps despite the lower pressure and these heaters are very efficient. Its a pity about they way the are fitted.

They are a mains fed heater and not designed to be tank fed, tank fed heaters at times can have their own problems usually over heating issues.

Safety valves like the one shown should be fitted on a t-piece with the inlet side capped leaving the cold mains side open for expansion they should never be fitted directly inline to the cold water inlet of the heater.

John T Carroll

gary71 wrote: »

The risk of the heater leaking/bursting is directly related to the incoming pressure, I find anything over 1 3/4 bar is more likly to have issues.

Firstly there is no regs and yours is a very very common installation that has at times caused 10s of thousands € worth of damage after the heaters burst.

The valve in your pic is usually rated at 8-9 bar and is a europeian valve and the one most commonly supplied/fitted, this is made more frightening when you look at plastic pipes reduced ability to deal with pressure as the heat increases leading to burst plastic pipes.

For your installation I'd advise fitting (towards the heater from the mains isolation valve) a pressure reducing valve if the water is over 3 1/2bar, a check valve/non-return valve, a 6 bar safety valve with a 1/2inch outlet so you can pipe the safety valve to terminate in a safe place with a tundish that doesn't allow water to leak if the valve opens and a expansion vessel to take up all expansion.

For the outlet I'm not a fan of plastic pipe and I like blending valves to protect users from potentially scalding themselves.

If this NRV is "just" an NRV then it doesnt matter how low the supply pressure is as long as it fills the heater with water, once the heater is switched on then the expansion simply has to be taken up by the hot water pipe?. If, as you impy, that this valve is supplied with the heater, then it is simply inviting plumbers to install it on top of the heater and thus leading to all sorts of problems, its very hard to fathom out why any reputable heater supplier would do this. My mains pressure is a constant 2.6 to 2.8 Bar at ground level so about 2.0 Bar at Attic level. I did carry out two more tests, one with everything as was for the past 12 years, I just switched on the heater until cut out point reached, I then isolated the supply water and opened the hot water tap and (obviously) nothing came out as the expansion was taken up by the main via the leaking NRV. I then switched off the heater, ran off all the hot water and shut an isolating valve which is approx 5 meters from the heater, I then switched on the heater again until cut out with the hot water valve shut, when I again opened the hot water tap, about 15CC came out so probably acceptable from a pressure point of view.
Thanks for your suggestions.

John T Carroll

Joe1919 wrote: »

I had a flood in a house lately caused by the expansion pressure blowing the pipe off the top of the heater with an Ariston undersink heater. The unit in the photo is a combined one way valve and pressure release valve and there is a problem when these are fitted on the heaters when no allowance is made for water expansion.(e.g. expansion vessel)
I was not happy with the way it was fitted and made some changes. The heater was moved to a built in wardrobe and is now is fed from a separate low pressure supply from the storage tank and the non-return element of the valve is not used. The heater feeds two wash hand basins and a kitchen sink and is now ventilated.I used copper pipes to connect to heaters but plastic on the runs to basins from the 't'.
There is a good flow to taps despite the lower pressure and these heaters are very efficient. Its a pity about they way the are fitted.

Thanks Joe, where is the link to the photo?. Personally, for home use, I would be happy to use these heaters with < 3.0 bar pressure from the mains as long as any NR and isolating valve are fitted not less than 5 meters from the heater, an overtemperature stat could/should be fitted as well, its mandatory now for years on the humble immersion heater.

John T Carroll

John T Carroll wrote: »

If this NRV is "just" an NRV then it doesnt matter how low the supply pressure is as long as it fills the heater with water, once the heater is switched on then the expansion simply has to be taken up by the hot water pipe?. If, as you impy, that this valve is supplied with the heater, then it is simply inviting plumbers to install it on top of the heater and thus leading to all sorts of problems, its very hard to fathom out why any reputable heater supplier would do this. My mains pressure is a constant 2.6 to 2.8 Bar at ground level so about 2.0 Bar at Attic level. I did carry out two more tests, one with everything as was for the past 12 years, I just switched on the heater until cut out point reached, I then isolated the supply water and opened the hot water tap and (obviously) nothing came out as the expansion was taken up by the main via the leaking NRV. I then switched off the heater, ran off all the hot water and shut an isolating valve which is approx 5 meters from the heater, I then switched on the heater again until cut out with the hot water valve shut, when I again opened the hot water tap, about 15CC came out so probably acceptable from a pressure point of view.
Thanks for your suggestions.

The installation of unvented under sink water heater is already very well documented under UK water regs but because they are UK water regs and not Irish water regs the installation requirements required due to physics and not nationality are mostly ignored as one installer put it to me" we're in Europe not bloody England".

You cannot use the hot water draw off pipe work for expansion calculations.

For a 10 ltr water heater 2.8 m of 1/2 inch pipe is required for expansion.

My point on in coming pressure is more to do with heater supplied with high mains pressure are more likely to burst due to the higher starting point of the cold water.

Yes those heaters come with those European 8/9 bar safety valves/non-return valves because they are for the greater European market, UK heaters come with a separate 6 bar safety valve and very precise fitting instructions.

It very easy to explain why things are the way they are €€€:eek:.

Installers and home owners in general don't wish to pay to fit them properly especially when they have themselves judged the risks of a heater bursting to be a risk not even worth talking about and in truth they are right but only because these heaters are connected to such low pressure mains, heater with pumped supplies or decent mains pressure have a different story to tell.

Joe1919

John T Carroll wrote: »

Thanks Joe, where is the link to the photo?. Personally, for home use, I would be happy to use these heaters with < 3.0 bar pressure from the mains as long as any NR and isolating valve are fitted not less than 5 meters from the heater, an overtemperature stat could/should be fitted as well, its mandatory now for years on the humble immersion heater.

I have attached link to photo. The pressure blew out the hot pipe and flooded the bathroom.
https://us.v-cdn.net/6034073/uploads/attachments/117066/348596.jpg

I still think there is a problem with the plumbing of these heaters, when they are unvented. The problem is with the non return valve. When fitted without an expansion vessel, it stops the water from expanding back along the cold feed and hence we can get a build up of pressure until the release valve opens. I also agree that the plastic pipes are not suitable for these type of pressures and temperatures.

Joe1919

Joe1919 wrote: »

I have attached link to photo. The pressure blew out the hot pipe and flooded the bathroom.
https://us.v-cdn.net/6034073/uploads/attachments/117066/348596.jpg

I still think there is a problem with the plumbing of these heaters, when they are unvented. The problem is with the non return valve. When fitted without an expansion vessel, it stops the water from expanding back along the cold feed and hence we can get a build up of pressure until the release valve opens.

Yours is a very common installation.

Unfortunately your pipe bursting was as much to do with the quality of the pipework as it was for the lack of provision for expansion.


They are unvented hot water heaters that have the potential to seriously damage people and property due to the temperature and pressures involved

Imagine now these heaters are fitted in schools, nurseries, crèche, public buildings without the basic safety precautions taken in to account or without anybody looking to determine the safety of the installation.

In the UK you have to pass a two day safety course called G3 which is mainly a course based on the risks involved giving installers a good understand of their responsibilities, very rarely will you see a undersink heater fitted unsafely in the UK, wouldn't it be nice if G3 was mandatory here to prevent heaters like yours bursting.

John T Carroll

Joe1919 wrote: »

I have attached link to photo. The pressure blew out the hot pipe and flooded the bathroom.
https://us.v-cdn.net/6034073/uploads/attachments/117066/348596.jpg

I still think there is a problem with the plumbing of these heaters, when they are unvented. The problem is with the non return valve. When fitted without an expansion vessel, it stops the water from expanding back along the cold feed and hence we can get a build up of pressure until the release valve opens. I also agree that the plastic pipes are not suitable for these type of pressures and temperatures.

Things are becoming alot clearer now, you have a combined NRV & PRV, yours has an "easing gear", a release handle whereas mine hasnt, the plastic push in/on elbows were no help either, its ironical that you have copper pipework but not brass compression fittings which just may have prevented the incident. It begs the question of course as to why the PRV didnt protect you particularly in view of the fact that the pressure doesnt build up rapidly, it takes about 18 minutes for a 2 Kw element to heat 10 Litres of water from say 10C to 60C. I would say that it must have been the PRV that saved me originally as the NR valve must have been tight and there was no place for the water to go. IF/when I have the energy I might remove it, test it and see what pressure it actually lifts at.

John T Carroll

gary71 wrote: »

They are a mains fed heater and not designed to be tank fed, tank fed heaters at times can have their own problems usually over heating issues.

Safety valves like the one shown should be fitted on a t-piece with the inlet side capped leaving the cold mains side open for expansion they should never be fitted directly inline to the cold water inlet of the heater.

I finally removed mine this morning and its most interesting as this isnt just a NRV but it also has another (the white one) smaller valve inside the (black) NR which acts in the opposite direction to equalise the pressures. Assume the valve is as in my case, installed directly to the cold water feed on top of the Heater, when water is being drawn off, the NRV complete with smaller equalising valve will open to allow water through the unit. If there is no draw off and the heater is switched in then the equalising valve will move very quickly off its seat in the opposite direction to the NRV and prevent any build up of pressure, after I had cleaned up all the components and reassembled it the equalising valve started passing (lifting) within two minutes of switching on the heater so this particular type/model can be fitted directly to the heater because of this arrangement, in my opinion. I don't know if all these valves are of the same type or not. The PRV seat is 8 to 8.5 MM dia. so would pass a big flow of water but what I don't really like is that the blow down connection has an ID of only 4.3 MM which is a bit surprising, maybe it will pass sufficient to keep the pressure in the system at/below say 8 Bar, in other words if the supply pressure went to 10 Bar for whatever reason then the flow through the PRV would only be equivalent to a head pressure of (10-8) 2 Bar.

Is the fitted valve in my case fit for purpose? I would have to say probably yes given that I have only 2 Bar pressure and my nearest cold water draw off on that line is greater than 3 meters from the Heater.
This "NRV" (it doesnt act like one) was possibly installed to help prevent heat loss from the heater to the cold water while also preventing excessive pressure build up due to expansion while the heater is on?.

John T Carroll

John T Carroll wrote: »

I finally removed mine this morning and its most interesting as this isnt just a NRV but it also has another (the white one) smaller valve inside the (black) NR which acts in the opposite direction to equalise the pressures. Assume the valve is as in my case, installed directly to the cold water feed on top of the Heater, when water is being drawn off, the NRV complete with smaller equalising valve will open to allow water through the unit. If there is no draw off and the heater is switched in then the equalising valve will move very quickly off its seat in the opposite direction to the NRV and prevent any build up of pressure, after I had cleaned up all the components and reassembled it the equalising valve started passing (lifting) within two minutes of switching on the heater so this particular type/model can be fitted directly to the heater because of this arrangement, in my opinion. I don't know if all these valves are of the same type or not. The PRV seat is 8 to 8.5 MM dia. so would pass a big flow of water but what I don't really like is that the blow down connection has an ID of only 4.3 MM which is a bit surprising, maybe it will pass sufficient to keep the pressure in the system at/below say 8 Bar, in other words if the supply pressure went to 10 Bar for whatever reason then the flow through the PRV would only be equivalent to a head pressure of (10-8) 2 Bar.

Is the fitted valve in my case fit for purpose? I would have to say probably yes given that I have only 2 Bar pressure and my nearest cold water draw off on that line is greater than 3 meters from the Heater.
This "NRV" (it doesnt act like one) was possibly installed to help prevent heat loss from the heater to the cold water while also preventing excessive pressure build up due to expansion while the heater is on?.

It would be interesting to know what your MI require.

For the Ariston it must be fitted on a tee piece leaving the cold side open for expansion, all the heaters that leak always have the valve screwed inline, heaters that have expansion taken into account have not leaked in the same manor.

Joe1919

Below is a link to the UK Ariston instruction manual.
www.ariston.com/uk/media/files/600_Europrisma%20Manual_V2.1.pdf

As far as I can recall, the Irish water heater has different instructions. ( I have lost the Irish instructions and I dont think they are on line.
From recollection of reading and inquiring, I think the non-return valve has 3 possible functions and of course has an additional pressure release function also built in. Note that the Ariston UK instruction do not recommend fitting nrv on top of heater as is the case in Ireland.

1 It prevents the heater from emptying ( & dry-boiling) in certain situations e.g. Water supply turned off, undersink heater upstairs, turning on tap could result in back syphoning to downstairs as cold inlet pipe goes down to bottom of tank.

2.It prevents from possible hot water expanding back into cold and been drawn off as (potable) drinking water, if placed near cold tap.

3. NRV is necessary in arrangement with expansion vessel, to prevent vessel from discharging back into main.

PS The pressure release valve (lever) also function to bleed the air out at installation.

John T Carroll

Joe1919 wrote: »

Below is a link to the UK Ariston instruction manual.
www.ariston.com/uk/media/files/600_Europrisma%20Manual_V2.1.pdf

As far as I can recall, the Irish water heater has different instructions. ( I have lost the Irish instructions and I dont think they are on line.
From recollection of reading and inquiring, I think the non-return valve has 3 possible functions and of course has an additional pressure release function also built in. Note that the Ariston UK instruction do not recommend fitting nrv on top of heater as is the case in Ireland.

1 It prevents the heater from emptying ( & dry-boiling) in certain situations e.g. Water supply turned off, undersink heater upstairs, turning on tap could result in back syphoning to downstairs as cold inlet pipe goes down to bottom of tank.

2.It prevents from possible hot water expanding back into cold and been drawn off as (potable) drinking water, if placed near cold tap.

3. NRV is necessary in arrangement with expansion vessel, to prevent vessel from discharging back into main.

PS The pressure release valve (lever) also function to bleed the air out at installation.

That all makes real sense now. Re your disaster, if the valve is/was a combined NRV/PRV (period) unlike my one, which, in view of your excellent info above, should now be called a combined Anti Syphon/Expansion Relief Valve/PRV?, then the vent from your valve should have expelled up to 150 CC of water every time that you heated the water to 60C from cold and one would think that you would have seen some evidence of this except that the PRV was seized or something. Have you still got this valve anywhere?, if you have it would be very interesting to see what it looks like.

Joe1919

Joe1919 wrote: »

Below is a link to the UK Ariston instruction manual.
www.ariston.com/uk/media/files/600_Europrisma%20Manual_V2.1.pdf

As far as I can recall, the Irish water heater has different instructions. ( I have lost the Irish instructions and I dont think they are on line.
From recollection of reading and inquiring, I think the non-return valve has 3 possible functions and of course has an additional pressure release function also built in. Note that the Ariston UK instruction do not recommend fitting nrv on top of heater as is the case in Ireland.

1 It prevents the heater from emptying ( & dry-boiling) in certain situations e.g. Water supply turned off, undersink heater upstairs, turning on tap could result in back syphoning to downstairs as cold inlet pipe goes down to bottom of tank.

2.It prevents from possible hot water expanding back into cold and been drawn off as (potable) drinking water, if placed near cold tap.

3. NRV is necessary in arrangement with expansion vessel, to prevent vessel from discharging back into main.

PS The pressure release valve (lever) also function to bleed the air out at installation.

The valve that comes with the Ariston heater is only to be fitted on a tee piece so only the safety valve part of the valve is used, it's not intended to be fitted inline which would then utilise the non-return part of the valve, the installer needs to take into account the perticular characteristics of heated pressurised water by dealing with expansion and fitting a non-return valve stopping any movement of hot water down the cold pipe when a cold tap before the heater is opened.

My advise is to fit it to fit it asper the fitting instruction because it's safer and it's also the benchmark used by insurance companies when look at insurance claims.

Joe1919

John T Carroll wrote: »

That all makes real sense now. Re your disaster, if the valve is/was a combined NRV/PRV (period) unlike my one, which, in view of your excellent info above, should now be called a combined Anti Syphon/Expansion Relief Valve/PRV?, then the vent from your valve should have expelled up to 150 CC of water every time that you heated the water to 60C from cold and one would think that you would have seen some evidence of this except that the PRV was seized or something. Have you still got this valve anywhere?, if you have it would be very interesting to see what it looks like.

I have attached a photo of similar valve. Interestingly, the hot tap always had a very slight drip, so perhaps this had relieved some of the pressure. The heater was left on all the time so the only time that there would be full expansion(from cold) was when all 10 liters of hot water was used.

John T Carroll

Joe1919 wrote: »

I have attached a photo of similar valve. Interestingly, the hot tap always had a very slight drip, so perhaps this had relieved some of the pressure. The heater was left on all the time so the only time that there would be full expansion(from cold) was when all 10 liters of hot water was used.

That link is exactly the same valve as I have (without the lever), if you look very closely at the left hand pic you will see that there is a "white" portion inside in a black surround, the white portion, as I have explained before is a spring (lightly) loaded valve that operates in the opposite fashion to the black portion which seats internally so this is NOT just a NRV as suggested by Garry above, I have explained above how all this works. Re drip from the hot tap, to me that means that excessive pressure had built up, for whatever reason, so even if the expansion relief (white bit) hadnt operated, then the PRV portion of this should still have protected you (as it lifts at 8.5 Bar) as the port for this is always in line with the cold water inlet at the point where the valve is screwed directly onto the heater, in other words its always sensing/measuring the internal pressure of the heater (including the hot water outlet) so should lift at 8.5 Bar.

Here is a link to an Ariston type, I will get one today and if I think its the same as my one then I will fit it, I wouldnt be happy to reinstall my one one now as I disassembled it a good few times and I removed the "tamperproof" plastic seal to get at the PRV pressure adjusting screw.
http://www.theheatxchange.co.uk/sku_ARI571730.html

John T Carroll

John T Carroll wrote: »

That link is exactly the same valve as I have (without the lever), if you look very closely at the left hand pic you will see that there is a "white" portion inside in a black surround, the white portion, as I have explained before is a spring (lightly) loaded valve that operates in the opposite fashion to the black portion which seats internally so this is NOT just a NRV as suggested by Garry above, I have explained above how all this works. Re drip from the hot tap, to me that means that excessive pressure had built up, for whatever reason, so even if the expansion relief (white bit) hadnt operated, then the PRV portion of this should still have protected you (as it lifts at 8.5 Bar) as the port for this is always in line with the cold water inlet at the point where the valve is screwed directly onto the heater, in other words its always sensing/measuring the internal pressure of the heater (including the hot water outlet) so should lift at 8.5 Bar.

Here is a link to an Ariston type, I will get one today and if I think its the same as my one then I will fit it, I wouldnt be happy to reinstall my one one now as I disassembled it a good few times and I removed the "tamperproof" plastic seal to get at the PRV pressure adjusting screw.
http://www.theheatxchange.co.uk/sku_ARI571730.html

If your going to reconnect your heater you'd be better off fitting a 6 bar UK safety valve with a tundish.

The Europian safety valve has a massive impact on the ability of the heater to deal with expansion so in respect of safety as Ariston advices they can be thought of as a non-return valve and is the reason for the excessive pressure which caused the dripping tap, when a heater is fitted with expansion taken in to account with a expansion vessel or the correct length of cold supply pipe then pressure from heating the water is not a issue ever.

Joe1919

John T Carroll wrote: »

That link is exactly the same valve as I have (without the lever), if you look very closely at the left hand pic you will see that there is a "white" portion inside in a black surround, the white portion, as I have explained before is a spring (lightly) loaded valve that operates in the opposite fashion to the black portion which seats internally so this is NOT just a NRV as suggested by Garry above, I have explained above how all this works. Re drip from the hot tap, to me that means that excessive pressure had built up, for whatever reason, so even if the expansion relief (white bit) hadnt operated, then the PRV portion of this should still have protected you (as it lifts at 8.5 Bar) as the port for this is always in line with the cold water inlet at the point where the valve is screwed directly onto the heater, in other words its always sensing/measuring the internal pressure of the heater (including the hot water outlet) so should lift at 8.5 Bar.

Here is a link to an Ariston type, I will get one today and if I think its the same as my one then I will fit it, I wouldnt be happy to reinstall my one one now as I disassembled it a good few times and I removed the "tamperproof" plastic seal to get at the PRV pressure adjusting screw.
http://www.theheatxchange.co.uk/sku_ARI571730.html

Thanks for the info. I did not realise that the valve worked in this way. I do think that 8.5 bar is a huge amount of pressure, and exceeds the rating of many plastic pipes at high temperatures. For example,

The following is a guideline as to what the operating parameters of Qual-PEX are;
12 Bar 20 ºC
4 Bar 82 ºC
3 Bar 92 ºC

http://www.pipelife.ie/ie/media/QPL_PDFs/Qual-PEX-FAQ.pdf

In my case, the bathroom hot water had been plumbed with plastic pipes and fittings and could not be changed easily as there was a hot pipe running under the shower tray that fed another toilet, which was tiled around and could not easily be taken out. I was unhappy with the workings and pressures and changed the whole lot over onto a low pressure storage tank, with its own feed off the tank. The NRV is not inline, but is on a 'T'. ( I am in agreement with Gary here I think.) Incidentally, the NRV wont work at low pressure anyhow because the low pressure (e.g 10 foot head is less than half a bar) would hardly lift the valve and the valve is narrow and restricts flow.

John T Carroll

gary71 wrote: »

If your going to reconnect your heater you'd be better off fitting a 6 bar UK safety valve with a tundish.

The Europian safety valve has a massive impact on the ability of the heater to deal with expansion so in respect of safety as Ariston advices they can be thought of as a non-return valve and is the reason for the excessive pressure which caused the dripping tap, when a heater is fitted with expansion taken in to account with a expansion vessel or the correct length of cold supply pipe then pressure from heating the water is not a issue ever.

I certainly respect what you (and Ariston) are saying but if "Ariston advices they can be thought of as a non-return valve" then they dont seem to know how a product that they are selling is supposed to work, as the NRV has an inbuilt expansion relief valve. I am just heading off now to pick up the 571730 replacement, I certainly wont be stripping this one down and in view of Joe,s and your comments/experience, I will install it, run cold water through it, remove the hot water outlet, attach a pressure gauge (just calibrated by a friend) note down the pressure at the start/end of heating cycle and report back, I certainly have no intention of flooding my house and if I have any reservations whatsoever I will certainly go down your suggested route, thanks.

John T Carroll

John T Carroll wrote: »

I certainly respect what you (and Ariston) are saying but if "Ariston advices they can be thought of as a non-return valve" then they dont seem to know how a product that they are selling is supposed to work, as the NRV has an inbuilt expansion relief valve. I am just heading off now to pick up the 571730 replacement, I certainly wont be stripping this one down and in view of Joe,s and your comments/experience, I will install it, run cold water through it, remove the hot water outlet, attach a pressure gauge (just calibrated by a friend) note down the pressure at the start/end of heating cycle and report back, I certainly have no intention of flooding my house and if I have any reservations whatsoever I will certainly go down your suggested route, thanks.

I find your information very interesting as in reality there is very little information on those European valves but without me sounding like a miserable sod the point of my original post is more to do with overall safety.

It much safer to fit these heaters to UK regs which leaves a much much safer installation, I often see heaters that would damage children if the safety valve lifts this cannot happen with UK regs.

If a European safety valve opens where does the discharge go?

Ariston advice is based on the things that go wrong and not the things that go right.

Heaters fitted with safety valves screwed directly on to the cold water inlet have more issues than those fitted on a T piece leaving the cold unrestricted, how many times would you need to witness that before you advised not to screw them inline?

John T Carroll

gary71 wrote: »

I find your information very interesting as in reality there is very little information on those European valves but without me sounding like a miserable sod the point of my original post is more to do with overall safety.

It much safer to fit these heaters to UK regs which leaves a much much safer installation, I often see heaters that would damage children if the safety valve lifts this cannot happen with UK regs.

If a European safety valve opens where does the discharge go?

Ariston advice is based on the things that go wrong and not the things that go right.

Heaters fitted with safety valves screwed directly on to the cold water inlet have more issues than those fitted on a T piece leaving the cold unrestricted, how many times would you need to witness that before you advised not to screw them inline?

Yes, of course if I was an installer working all over the place, and not knowing what the various pressures are/were likely to be in all the various establishments then its without doubt safer/wiser to go reducing set/ expansion vessel/6 bar full bore PRV and in line NRV. In view that Ariston now have concerns then presumably they do not include the 571730 valve now either supplied with their heaters or in kit form??.

John T Carroll

Joe1919 wrote: »

Thanks for the info. I did not realise that the valve worked in this way. I do think that 8.5 bar is a huge amount of pressure, and exceeds the rating of many plastic pipes at high temperatures. For example,

http://www.pipelife.ie/ie/media/QPL_PDFs/Qual-PEX-FAQ.pdf

In my case, the bathroom hot water had been plumbed with plastic pipes and fittings and could not be changed easily as there was a hot pipe running under the shower tray that fed another toilet, which was tiled around and could not easily be taken out. I was unhappy with the workings and pressures and changed the whole lot over onto a low pressure storage tank, with its own feed off the tank. The NRV is not inline, but is on a 'T'. ( I am in agreement with Gary here I think.) Incidentally, the NRV wont work at low pressure anyhow because the low pressure (e.g 10 foot head is less than half a bar) would hardly lift the valve and the valve is narrow and restricts flow.

The storage tank suppy is a good practical idea. I purchased and fitted the "571730" valve today, I ran water through the heater and then removed the hot water line and attached the pressure gauge directly to the heater. The start pressure was 3.0 Bar, I switched on the heater and the pressure went to 3.6 Bar after 2 minutes and finally settled at 4.0 Bar after 3.5 minutes and stayed exactly there up to the end of the 17 minute heating period. This means that the expansion relief valve needs a differential pressure of 1.0 Bar to start opening, to test the anti syphon function I shut off the mains downstairs and opened a few downstairs taps to drain the system rapidly and create a syphoning effect. The pressure then had fallen to 1.0 Bar and remained there for a 1/2 hour monitoring period, this also is correct as the expansion relief valve does not close until the differential pressure is less than 1.0 Bar.
I live at one of the highest points in Cork and as my system is reservoir fed then the pressure will never rise above 3 to 3.5 Bar depending on usage downstream of me ( its generally is around 2.5 to 2.8 Bar at ground level) so I am fairly happy that this valve will do the job for me as the other one did for the past 12 years......however I have taken on board both yours and Gary's comments and I will T in a 6 Bar PRV and drain tundish as I also dont like the 8.5 Bar PRV even though my system can "never" reach even 4 Bar in my opinion.

Here is a link to the installation of Electric Water Heaters which is fairly well written. http://www.hygienesuppliesdirect.com/products/productdata/product_notes.pdf