Hot water cylinder temp

5500

Hi Guys
Looking for some info regarding the above.

I have a 140litre quick recovery insulated cylinder and worchester greenstar boiler along with 3 zone controls.

The water is set to heat for about 3 hours a day and is predominantly used for washing up, no baths ect but the highest the thermostat ever shows for the cylinder is around 48degrees.

The thermostat is right onto the cylinder in a small cutout of the foam and sealed over, on the bottom third of it.

The actual temp is set at 62degrees on the boiler itself.

I've read about the lower temps possibility of causing listeria so I'm wondering what I can do to get the temp safely higher, or is my only option to run it for longer or increase temp on the boiler itself?

I know there's a blending valve at the cylinder itself but is that solely for water coming out of the tank or can it also affect the temp within the tank itself?

Any suggestions appreciated!

Sleeper12

Heat rises. If its 48 two thirds down then it should be 60 or more at the top of the cylinder I would think.

John.G

You say "the highest the thermostat ever shows for the cylinder is around 48degrees."
So are you saying that the tank thermostat is set to 48C?, if so, then increase this to 60C or very slightly above and inctrease the boiler set point to 65/70C, if the cylinder thermostat is already set to 60C and you are only getting 48C hot water then another problem.
The water in the cylinder should be heated to 60C at least once per week AFAIK to prevent legionella but apart from that if you do heat 140 litres to 60C then you will get 233 litres of hot water at 40C, (assuming cold water at 10C), useful for multiple showers without relying completely on your rapid recovery coil, if the water is only heated to 48C then you will only get 177 litres of hot water at 40C.

If the cylinder stat is set to 60c and you are only heating to 48C, then just turn the stat anti clockwise until you hear a click, its setting should closely correspond to the cylinder temperature at the point where the cylinder stat is attached, if you turn it very slowly clockwise, you should hear another click after increasing the setting by ~ 5C, if test satisfactory, return the setting to 60C.

Also ensure that that the cylinder stat is installed above the coil return as it probably is, if on the "bottom third".

5500

The stat for the cylinder is set to knock off at 62, although it never reaches this, the highest it gets to when the water is on for say 3 hours is 48/49 (its an eph ember digital stat, with the probe attached to cylinder)

John.G

That cylinder should heat up to 60C in well less than a hour, probably 30/45 mins max, probably a problem with that stat, you will find a motorized valve on the supplyy to the coil, you can easily check if its opening/closing from the stat, just increase the stat setpoint to 90C and it should go fully open, then reduce it to 10C and it should shut, if you also do what I suggested originally you probably should also hear the contacts opening/closing around the actual cylinder temperature. If CH is not selected then you should also hear the boiler firing up when the cylinder only calls for heat.

Lenar3556

Assuming the reading on the EPH thermometer is correct, you need to get the cylinder temperature up, if for no other reason than to avoid legionella.

I think the boiler temp is too low, there will be losses between the boiler and the cylinder so you need to have the boiler temp the better part of 10 degrees higher than the desired cylinder temp so it it can comfortably reach it in a timely manner and stop the call for heat on the boiler.

Blending valves would be better fitted at individual outlets/taps, rather than one global control. Also for reasons of legionella.

That is probably a well insulated cylinder, and all losses are going to be into the house anyway. I would probably leave it on 24hrs, with just the temperature control managing it.

GreeBo

What temp are the outlet pipes at?
What temp is the water when it leaves the taps?

Lenar3556

Just looked at the EPH website and see what I think is the thermostat with probe. If this is a retro fit job simply stuck onto the side of the cylinder where insulation has been removed, there is considerable scope for an inaccurate reading. Even in a best case scenario, great care needs to be taken when position cylinder stats - fully remove insulation, use conductive compound etc.

For an accurate reading, a cylinder like that would benefit from a thermostat pocket, which went right into the body of the cylinder.

Lenar3556

GreeBo wrote: »

What temp are the outlet pipes at?
What temp is the water when it leaves the taps?

I think he mentioned he had a blending valve installed at the cylinder.

John.G

Lenar3556 wrote: »

Just looked at the EPH website and see what I think is the thermostat with probe. If this is a retro fit job simply stuck onto the side of the cylinder where insulation has been removed, there is considerable scope for an inaccurate reading. Even in a best case scenario, great care needs to be taken when position cylinder stats - fully remove insulation, use conductive compound etc.

For an accurate reading, a cylinder like that would benefit from a thermostat pocket, which went right into the body of the cylinder.

That certainly wouldn't give a accurate cylinder temperature, I have seen a RF cylinder stat that was mounted on the "wall" with a probe on the end of a cable, the cylinder had a dry pocket into which the probe was inserted, A normal stat is strapped onto and is in close contact to the cylinder.

KingCong

John.G wrote: »

I have seen a RF cylinder stat that was mounted on the "wall" with a probe on the end of a cable, the cylinder had a dry pocket into which the probe was inserted, A normal stat is strapped onto and is in close contact to the cylinder.

I have this also with a 300L Kingspan factory insulated solar tank and have a similar issue to the OP. When the probe is inserted into the hole 1/3 of the way from top it gets to 60C within an hour, however when the probe is inserted in the hole 1/3 of the way from the bottom it never gets to 60C, no matter how long the boiler is on. I think this is because its a solar tank though we don't have solar tubes (solar tank installed to be future proof but that's another story), and the plumbers have the return pipe from the tank connected to the pipe outlet half way up the tank, just above where the temp probe is.

So with heat rising only the top half of the tank is being heated and the probe never gets to 60C. Would this make sense? And shouldn't the plumbers have connected the H/W loop from the boiler to the solar coil at the bottom when there's no solar panels installed? Effectively our 300L tank is only around 150L of usable H/W.

John.G

Yes, that makes perfect sense, the solar coil is in the bottom of the cylinder and will heat all the tank if enough "sun" is available but the oil/gas boiler will only heat the top "1/2". With no solar installed the two coils should be in series with the boiler flow entering at the top, passing down through the boiler coil and then on down through the solar coil and returned to the boiler, you can then leave the probe in its present pocket or insert in in the solar pocket, the solar pocket IMO is the best place as the boiler will start reheating the cylinder sooner as the cold water passes up through the cylinder when hot water is being drawn off and will hit the solar pocket first.

KingCong

John.G wrote: »

Yes, that makes perfect sense, the solar coil is in the bottom of the cylinder and will heat all the tank if enough "sun" is available but the oil/gas boiler will only heat the top "1/2". With no solar installed the two coils should be in series with the boiler flow entering at the top, passing down through the boiler coil and then on down through the solar coil and returned to the boiler, you can then leave the probe in its present pocket or insert in in the solar pocket, the solar pocket IMO is the best place as the boiler will start reheating the cylinder sooner as the cold water passes up through the cylinder when hot water is being drawn off and will hit the solar pocket first.

Thanks for the reply. So just to confirm with regards to Legionella, with the current way its set up with the top half of the tank getting to the 60c but the bottom half not, is this safe? Assuming it is since the water leaves from the top of the tank for showers/taps and any bacteria at the bottom of the tank would likely be heated/killed before left the tank?

5500

Lenar3556 wrote: »

Just looked at the EPH website and see what I think is the thermostat with probe. If this is a retro fit job simply stuck onto the side of the cylinder where insulation has been removed, there is considerable scope for an inaccurate reading. Even in a best case scenario, great care needs to be taken when position cylinder stats - fully remove insulation, use conductive compound etc.

For an accurate reading, a cylinder like that would benefit from a thermostat pocket, which went right into the body of the cylinder.

John.G wrote: »

That certainly wouldn't give a accurate cylinder temperature, I have seen a RF cylinder stat that was mounted on the "wall" with a probe on the end of a cable, the cylinder had a dry pocket into which the probe was inserted, A normal stat is strapped onto and is in close contact to the cylinder.

Your both right there, the probe is on a cable where a piece of insulation was removed, the lenght of the probe is then "stuck" to the tank as opposed to it being just the tip touching it if that makes sense, and then backfilled in.

Just to add I also did check that the valve was working with the stat, eg it'll open/close fully when you adjust the temp on the actual stat and fire boiler ect

I have an IR thermometer there and could check temp at the top of the cylinder with that if it makes a difference, but I'll increase temp on the boiler to 70 and see what that comes back with too

John.G

I would think that with that set up that the probe is reading low all the time and your tank is actually roasting and at the same temperature as the boiler but you don't notice it because of the mixing valve.
That will never work accurately, I would throw it out and either buy a traditional contact type stat with a rotary dial or you may be able to buy a digital contact type, just ensure that it is installed about 6 ins above the coil return.

John.G

KingCong wrote: »

Thanks for the reply. So just to confirm with regards to Legionella, with the current way its set up with the top half of the tank getting to the 60c but the bottom half not, is this safe? Assuming it is since the water leaves from the top of the tank for showers/taps and any bacteria at the bottom of the tank would likely be heated/killed before left the tank?

I think you should be OK because any legionella will originate normally in the cold water storage tank so makes no difference really, also, even if you heat the whole tank there will still be 20 litres or so of unheated water in the bottom of the cylinder.
There are thousands of electric dual immersion heated HW cylinders where the sink immersion is used (heating only ~ 30 litres) for the whole summer (like my own, before I installed a modest solar system) and I don't see any recommendations as to their non use.

dathi

John.G wrote: »

I think you should be OK because any legionella will originate normally in the cold water storage tank so makes no difference really, also, even if you heat the whole tank there will still be 20 litres or so of unheated water in the bottom of the cylinder.
There are thousands of electric dual immersion heated HW cylinders where the sink immersion is used (heating only ~ 30 litres) for the whole summer (like my own, before I installed a modest solar system) and I don't see any recommendations as to their non use.

what i find funny is the amount of people who are quite happy to shower in a tank fed triton shower that raises the water to mid 40s degrees at best but will insist on 60 degrees for the cylinder

John.G

I would agree, even if you wised to "sterilise" your electric shower at 60C you simply can't as all showers have a TCO which will trip the heating elements at 48C (for very good safety reasons). A mains fed shower is theoretically safer as the cold water has no residence time whereas the tank fed shower is fed from a cold water storage tank which can easily reach 23/25C in summer.
Thermal stores often have a DHW coil installed, the cold water simply flows through the coil (no residence time ) so can be used at any temperature.

I think some ASHP only heat the DHW to 60C once per week for efficiency reasons.

Lenar3556

dathi wrote: »

what i find funny is the amount of people who are quite happy to shower in a tank fed triton shower that raises the water to mid 40s degrees at best but will insist on 60 degrees for the cylinder

Electric showers are considered low risk, because water is not stored for any period at temperatures which allow legionella to grow.

The difficulty arises when water is stored for long periods at 25-45ish degrees. Under temperature hot water cylinders being the classic example.

It’s not a huge issue in Ireland, yet 15 or so people are hospitalised with the disease annually. Symptoms are not unlike pneumonia and can be fatal.

GreeBo

dathi wrote: »

what i find funny is the amount of people who are quite happy to shower in a tank fed triton shower that raises the water to mid 40s degrees at best but will insist on 60 degrees for the cylinder

The water in the cold storage tank is replaced when either the hot or cold water is used anywhere in the house.
The water in the cylinder is only replaced when hot water is used.

So the electric shower is using fresher water than the cylinder.

dathi

GreeBo wrote: »

The water in the cold storage tank is replaced when either the hot or cold water is used anywhere in the house.
The water in the cylinder is only replaced when hot water is used.

So the electric shower is using fresher water than the cylinder.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5896965/

if you have time read this report or here is part of the conclusions

According to our results, and withfew exceptions, water temperature, the level of sedimentation and biofilm (known risk factors for the establishment of Legionella and other water bourne pathogens) increased in quantity/severity between UBV and FE in both cold water and potable water storage tanks. Consequently, 20% of the tanks surveyed failed to trigger appropriate regulatory action based on microbiological analyses of the water sample taken under the ball valve compared to the far end sample using present-day standards. These results call into question the reliability of present measures used to protect the public from water bourne pathogenic diseases, including Legionella.

GreeBo

dathi wrote: »

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5896965/

if you have time read this report or here is part of the conclusions

According to our results, and withfew exceptions, water temperature, the level of sedimentation and biofilm (known risk factors for the establishment of Legionella and other water bourne pathogens) increased in quantity/severity between UBV and FE in both cold water and potable water storage tanks. Consequently, 20% of the tanks surveyed failed to trigger appropriate regulatory action based on microbiological analyses of the water sample taken under the ball valve compared to the far end sample using present-day standards. These results call into question the reliability of present measures used to protect the public from water bourne pathogenic diseases, including Legionella.

Thx for that, I did often wonder about all the sediment, etc you see around water tanks...

Their conclusion seems strange though.
They are calling for better access to the far end of the tanks.
All thats going to do is prove what they believe they have already demonstrated?

I would have thought the conclusions should be something along the lines of "cold water storage tanks currently dont offer adequate protection against x, y, z and we recommend a, b, c"