Cylinder heating but rads wont

Paul_Mc1988 · 22-02-2020 3:20am #1

Hi guys,

Bought a house recently and have done a whole home renovation but left the main heating system mainly untouched (due to budget). House is a three bed semi D

I added one rad onto the existing system. Upstairs has four rads. One in each bedroom and the bathroom. Downstairs has a rad in the hall, a rad in the living room and rad in the kitchen/dinner ( this is the new rad as there was previously gas fires in here). I removed all rads and fitted TRVs on them. I also installed two motorized valves at the boiler.

When I turn on the cylinder circuit the water gets up to the cylinder and the return pipe at the boiler gets warm quite quick ( 5minutes). When I turn on the radiator circuit some of the rads are getting luke warm others not at all. The inlet pipe to the rads is hot but the outlet either cold or luke warm. I have bled all the rads numerous times but no joy. Any ideas. The pump is a myson and probably there since the original install 20+ years. Boiler is a worchester condensing boilerThinking the pump may be struggling and on it's way out. Any ideas?

Turbohymac · 22-02-2020 3:32am

Possibly the water is taking the path of least resistance and simply coming in from your boiler and heading up those nice big 3/4 pipe to your hot cylinder and returning as easy back to the boiler..I had this same issue but I had to put an inline valve before the cylinder to cause less flow and more resistance which meant I had extra pressure and flow to force the water around the much smaller pipework and valves of my radiator circuit as i am only using 1 circulation pump..
Also rethink has this always been an issue or maybe you have caused extra restrictions on your rad circuit..
Good luck..

Paul_Mc1988 · 22-02-2020 6:56am

Turbohymac wrote: »

Possibly the water is taking the path of least resistance and simply coming in from your boiler and heading up those nice big 3/4 pipe to your hot cylinder and returning as easy back to the boiler..I had this same issue but I had to put an inline valve before the cylinder to cause less flow and more resistance which meant I had extra pressure and flow to force the water around the much smaller pipework and valves of my radiator circuit as i am only using 1 circulation pump..
Also rethink has this always been an issue or maybe you have caused extra restrictions on your rad circuit..
Good luck..

Had also thought about that. The rad is a 3/4 inch too for the first 4 meters and it splits to 1/2 inch for the upstairs and downstairs. With the motorized valves in place only one direction opens so when I select heating that valve opens and then the boiler and pump come on so the only direction is the radiator direction. Thanks for the input

.

Come to think of it when I have both motorized valves open the water only goes to the cylinder so it's looking more like a pump strength issue. Can you just put on a more powerful pump. Mine has two RPM settings and it's set to the higher setting already.

Turbohymac · 22-02-2020 11:21am

Ok.. like my earlier post
.forget about upgrading pump etc..a pump can only create a certain amount of flow but try to restrict the flow through your hot cylinder and your rads will then benefit...ideally you should actually be passing the water through the cylinder first ..to heat the water..then onwards to the radiators..but in your setup you need to restrict flow way down going to cylinder....it only needs a fraction of flow to heat the water. Not full flow.. put a lever valve inline to cylinder and shut it down half.. your rads should then be fine.. also you might even have to restrict the nearest rad to your boiler as the same principle applies..sometimes the furthest away rad can suffer from lack of adequate hot water flowthrough..
I think you're near sorted..dont bother replacing pumps etc ..just restrict..

John.G · 22-02-2020 1:19pm

Paul_Mc1988 wrote: »

Hi guys,

Bought a house recently and have done a whole home renovation but left the main heating system mainly untouched (due to budget). House is a three bed semi D

I added one rad onto the existing system. Upstairs has four rads. One in each bedroom and the bathroom. Downstairs has a rad in the hall, a rad in the living room and rad in the kitchen/dinner ( this is the new rad as there was previously gas fires in here). I removed all rads and fitted TRVs on them. I also installed two motorized valves at the boiler.

When I turn on the cylinder circuit the water gets up to the cylinder and the return pipe at the boiler gets warm quite quick ( 5minutes). When I turn on the radiator circuit some of the rads are getting luke warm others not at all. The inlet pipe to the rads is hot but the outlet either cold or luke warm. I have bled all the rads numerous times but no joy. Any ideas. The pump is a myson and probably there since the original install 20+ years. Boiler is a worchester condensing boilerThinking the pump may be struggling and on it's way out. Any ideas?

Its not quite clear to me if one zone valve just feeds the cylinder coil circuit and the other zone valve feeds both the up and down stairs rads?. if so, or even not, it certainly won't be throwing away money in renewing the pump especially if you can install it yourself, I might suggest a DAB Evosta 4/7M, or (like my own) a Wilo Yonos Pico 1/6M. I have 8 double rads+2 singles and the pump on a 3M head (equivalent) can feed the 10 rads plus the hot water cylinder no problem, I do have a balancing valve on the cylinder coil but have never had to throttle it in, in > 40 years.

Paul_Mc1988 · 22-02-2020 3:03pm

John.G wrote: »

Its not quite clear to me if one zone valve just feeds the cylinder coil circuit and the other zone valve feeds both the up and down stairs rads?. if so, or even not, it certainly won't be throwing away money in renewing the pump especially if you can install it yourself, I might suggest a DAB Evosta 4/7M, or (like my own) a Wilo Yonos Pico 1/6M. I have 8 double rads+2 singles and the pump on a 3M head (equivalent) can feed the 10 rads plus the hot water cylinder no problem, I do have a balancing valve on the cylinder coil but have never had to throttle it in, in > 40 years.

Yeah one zone feed the coil and the other zone the upstairs and downstairs rads.

I'll have a look at them pumps cheers for the help everyone. Be back on soon if I have any further issues

Wearb · 22-02-2020 3:31pm

Take off all the TRV heads. Make sure the pin on the valves moves freely. It only moves a few mm. If they are working, leave them off, turn cylinder zone off and Heating zone on. With this done, check that cylinder isn't heating and report back here on how the rads are heating.

Paul_Mc1988 · 22-02-2020 5:04pm

Wearb wrote: »

Take off all the TRV heads. Make sure the pin on the valves moves freely. It only moves a few mm. If they are working, leave them off, turn cylinder zone off and Heating zone on. With this done, check that cylinder isn't heating and report back here on how the rads are heating.

Will do this when I'm in the house tomorrow. Thanks Wearb.

John.G · 22-02-2020 5:36pm

Also problem may have started with zone valves & TRVs installation, check that rads zone valve is pointing in right direction and is opening fully, its also possibly a pipework sludge problem but you would have seen this when the rads were removed. Air locks in system? maybe consider draining down system and refilling slowly with boiler switched off and both zone valves manually latched open to assist proper venting. (this is often overlooked).

Paul_Mc1988 · 23-02-2020 1:08pm

John.G wrote: »

Also problem may have started with zone valves & TRVs installation, check that rads zone valve is pointing in right direction and is opening fully, its also possibly a pipework sludge problem but you would have seen this when the rads were removed. Air locks in system? maybe consider draining down system and refilling slowly with boiler switched off and both zone valves manually latched open to assist proper venting. (this is often overlooked).

What do you mean by the rad zone valve pointing in the right direction?

John.G · 23-02-2020 1:20pm

There will be a arrow stamped on the body of the zone valve, ensure that the flow corresponds to this.

crossmolinalad · 24-02-2020 2:42pm

Flushing the rads system did the trick here
Pipes were full of muck

Paul_Mc1988 · 24-02-2020 4:51pm

Got it sorted. Thanks everyone for the help. System just had a lot of air locks. Closed of all the rads valves. And started heating them one by one. Took about three hours to get it fully done. All rads piping hot.

One final query. The boiler is a worchester 15i condensing. How long after turning the heating off should it keep running the pump for? Is this an over run safety thing so hot water doesn't boil over in the boiler?

John.G · 24-02-2020 8:53pm

Its to protect the boiler heat exchanger which is often made of aluminium, when you shut down the boiler then both zone valves close and the water will have no where to go except that (1) you have fitted a automatic bypass valve (ABV) or (2) you have plumbed in one rad with its flow taken upstream of the zone valve or (3) the boiler itself has a internal by pass which will eventually cool down the water but will take a long long time, your user manual will tell you if you have one. The pump overrun time would be ~ 2 to 5 minutes but some boilers keep the pump running until it sees the water temperature falling. I think some of the older boilers just kept running the fan for a certain period to achieve this cool down.

Paul_Mc1988 · 25-02-2020 8:36pm

John.G wrote: »

Its to protect the boiler heat exchanger which is often made of aluminium, when you shut down the boiler then both zone valves close and the water will have no where to go except that (1) you have fitted a automatic bypass valve (ABV) or (2) you have plumbed in one rad with its flow taken upstream of the zone valve or (3) the boiler itself has a internal by pass which will eventually cool down the water but will take a long long time, your user manual will tell you if you have one. The pump overrun time would be ~ 2 to 5 minutes but some boilers keep the pump running until it sees the water temperature falling. I think some of the older boilers just kept running the fan for a certain period to achieve this cool down.

Hi John. Yeah the pump is running for a few minutes when both valves are closed. Will this damage the pump if the water has nowhere to go?. I dont have a rad upstream of the valves either!

John.G · 25-02-2020 10:02pm

There should really be a pathway for the water during this pump overrun, I'd be more concerned with the boiler rather than the pump. you might consider the installation of a ABV, (instead, you could plumb in one rad flow upstream of the zone valve but that really defeats the purpose of zoning in the first place and the rad would have to be manually shut off during the summer months when hot water only required.)
I would first try and establish if your boiler has, in fact. a internal by pass, I don't know if your boiler is relatively new or is as old as your circ pump but one way or the other its unlikely to have a st.steel heat exchanger and it would certainly IMO, be very prudent to install that ABV.

It's a pity that there isn't some way electrically of opening say the hot water zone valve on pump overrun without re firing the boiler but I can't see how this can be done with a "S" plan system.

https://www.plumberparts.co.uk/advice/heating-systems/s-plan-heating-system

Paul_Mc1988 · 25-02-2020 10:32pm

John.G wrote: »

There should really be a pathway for the water during this pump overrun, I'd be more concerned with the boiler rather than the pump. you might consider the installation of a ABV, (instead, you could plumb in one rad flow upstream of the zone valve but that really defeats the purpose of zoning in the first place and the rad would have to be manually shut off during the summer months when hot water only required.)
I would first try and establish if your boiler has, in fact. a internal by pass, I don't know if your boiler is relatively new or is as old as your circ pump but one way or the other its unlikely to have a st.steel heat exchanger and it would certainly IMO, be very prudent to install that ABV.

It's a pity that there isn't some way electrically of opening say the hot water zone valve on pump overrun without re firing the boiler but I can't see how this can be done with a "S" plan system.

https://www.plumberparts.co.uk/advice/heating-systems/s-plan-heating-system

There is way it could be done electrically with some simple relay logic by use of the feed to the pump and some NO and NC contacts. Would just need to sit down with some paper over the next few days and work it out.

John.G · 25-02-2020 10:38pm

That would be great Paul and very interesting to see how you can do it, I'm a bit surprised it hasn't been configured by the boiler manufacturers or whoever, before.

John.G · 29-02-2020 9:51pm

Paul_Mc1988 wrote: »

There is way it could be done electrically with some simple relay logic by use of the feed to the pump and some NO and NC contacts. Would just need to sit down with some paper over the next few days and work it out.

Here's one?? from my archive's.

Paul_Mc1988 · 02-03-2020 8:18pm

John.G wrote: »

Here's one?? from my archive's.

Thanks John you a star. That will save me a bit of hassle.:)

You wouldn't have a link to where i could get the relays in question?

John.G · 02-03-2020 8:46pm

Sorry, no I havn't.

03-03-2020 12:22am

I’d keep it simple and fit a external auto bypass, no wires required

John.G · 03-03-2020 10:01am

Yes, I like KIS myself but as Paul is probably electrically qualified then he should have no problem in configuring this and would be interesting to see how it works out. (go on Paul!)

Unfortunately, with the advent of smart circulating pumps which can be run in a number of different modes, a ABV is now not suitable in a lot if not most cases as previously the circ pump only had constant curve/fixed speed settings so it was relatively simple to set up the ABV to only open when all the zone valves close and the pump head rises, most of these pumps now however do NOT have true constant curve modes as they actually act like constant pressure mode up to about 0.4/0.6 m3/hr, 7/10 LPM, so the ABV will pass excessively or not at all depending on its setting, if constant pressure mode is selected then a fixed by pass flowrate will have to be accepted at all times, if proportional pressure is selected then the ABV, if set up towards the lower PP head will again pass excessively at the higher end.
However, one of the pumps I recommended above, the DAB Evosta, does have true constant curves (as does Paul's veteran pump) but even though the ABV would work perfectly well with the DAB on constant curve it means that you cannot run in CP or PP mode which is a shame as there are nice savings in either of these modes. Also system gas boilers have their own custom built pumps and some of these can be user selected to run in different modes so again very difficult to set up the traditional ABV.
In view of this, IMO, the only logical way to cater for all of the above is that the boiler manufacturer should provide a volt free relay that is only energised when the pump is on overrun, a 3/4 ins motorized valve should be fitted between the flow and return which when wired in via the relay will open during the pump overrun and reclose when the overrun ceases, it doesn't matter then what head the pump is providing in any mode as a fully open motorized valve will provide a very adequate flowrrate under any conceivable pump setting.
Again, of course, maybe some do provide this, and so they should, as smart A rated circ pumps are out for ~ 10 years now?

03-03-2020 10:40am

John.G wrote: »

Yes, I like KIS myself but as Paul is probably electrically qualified then he should have no problem in configuring this and would be interesting to see how it works out. (go on Paul!)

Unfortunately, with the advent of smart circulating pumps which can be run in a number of different modes, a ABV is now not suitable in a lot if not most cases as previously the circ pump only had constant curve/fixed speed settings so it was relatively simple to set up the ABV to only open when all the zone valves close and the pump head rises, most of these pumps now however do NOT have true constant curve modes as they actually act like constant pressure mode up to about 0.4/0.6 m3/hr, 7/10 LPM, so the ABV will pass excessively or not at all depending on its setting, if constant pressure mode is selected then a fixed by pass flowrate will have to be accepted at all times, if proportional pressure is selected then the ABV, if set up towards the lower PP head will again pass excessively at the higher end.
However, one of the pumps I recommended above, the DAB Evosta, does have true constant curves (as does Paul's veteran pump) but even though the ABV would work perfectly well with the DAB on constant curve it means that you cannot run in CP or PP mode which is a shame as there are nice savings in either of these modes. Also system gas boilers have their own custom built pumps and some of these can be user selected to run in different modes so again very difficult to set up the traditional ABV.
In view of this, IMO, the only logical way to cater for all of the above is that the boiler manufacturer should provide a volt free relay that is only energised when the pump is on overrun, a 3/4 ins motorized valve should be fitted between the flow and return which when wired in via the relay will open during the pump overrun and reclose when the overrun ceases, it doesn't matter then what head the pump is providing in any mode as a fully open motorized valve will provide a very adequate flowrrate under any conceivable pump setting.
Again, of course, maybe some do provide this, and so they should, as smart A rated circ pumps are out for ~ 10 years now?

I can’t stop some sparks using the boilers Earth wire to carry switch lives let alone getting them to wire a extra switch live to dissipate heat to fix a problem that is rectified with a simple auto bypass.

Paul_Mc1988 · 03-03-2020 12:22pm

gary71 wrote: »

I can’t stop some sparks using the boilers Earth wire to carry switch lives let alone getting them to wire a extra switch live to dissipate heat to fix a problem that is rectified with a simple auto bypass.

As a sparks it's easy for me to rectify and cheaper than getting a plumber. House is only just at the second fix stage and I wired extra feeds for future proofing. It's my house and my boiler so ensuring it works safely and correctly is in my best interest.

03-03-2020 1:03pm

Paul_Mc1988 wrote: »

As a sparks it's easy for me to rectify and cheaper than getting a plumber. House is only just at the second fix stage and I wired extra feeds for future proofing. It's my house and my boiler so ensuring it works safely and correctly is in my best interest.

Identifying faults on domestic gas heating systems is my day job and as a city and guilds gas service engineer with enough experience to make me very very grumpy I’d advise fitting a bypass because that is the correct proven response to a very common problem.

John.G · 12-06-2020 11:38am

Paul_Mc1988 wrote: »

Thanks John you a star. That will save me a bit of hassle.:)

You wouldn't have a link to where i could get the relays in question?

Just came across this thread again and wondered if you modified the system to give you a by pass?.

Thinking about it again, there is a much simpler solution without all those timers/relays but does involve the installation of a piece of 1/2 ins piping between the flow and return and a normally open (NO) 2 port valve like a Honeywell V4043B, you simply wire from both zone valve end switches (orange? wires) to the above valve. If either (or both) of the zone valves open then the bypass will close and when both zone valves close then the by pass will open.

Cylinder heating but rads wont

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