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Hot outlet calorifier mixed with cold?


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Hi!
When I close the tap right at the outlet on top of my calorifier my taps still run water: cold water! It seems that the outlet pipe somewhere in my floor (which I don't really have easy access to unfortunately) is getting mixed with a cold water circuit input again, before going to my taps! Or perhaps something more complicated is going on. I don't see any logic in this. Would you have any idea why this is the case? Or would this be a silly installation mistake?

 

The diagram on this page about domestic water systems (just above "SIMPLE OPERATION") doesn't suggest these complications...

http://www.tb-training.co.uk/17Bdomwat.html

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17 minutes ago, AndrewIC said:

Thermostatic mixing valve somewhere to prevent scalding?

There is often one on the top of the calorifier turn it right down and you will get cold water out ;)

Its the black one in this picture the red one is the PRV

 

520322.jpg

Edited by Loddon
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14 minutes ago, AndrewIC said:

Thermostatic mixing valve somewhere to prevent scalding?

The most common type looks like this. Very hot water from the cauliflower, mixing in cold water to a set temperature. If there is no hot in, possible it may flow cold. Don't know, never tried it.

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I’ve had shower mixing valves and also mixer taps passing in domestic properties, if you have isolation valves accessible going to any of these  try turning them off and if the water stops running that’s possibly where the problem lies, good luck 🤞 

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1 hour ago, Njiruk said:

Hi!
When I close the tap right at the outlet on top of my calorifier my taps still run water: cold water! It seems that the outlet pipe somewhere in my floor (which I don't really have easy access to unfortunately) is getting mixed with a cold water circuit input again, before going to my taps! Or perhaps something more complicated is going on. I don't see any logic in this. Would you have any idea why this is the case? Or would this be a silly installation mistake?

 

The diagram on this page about domestic water systems (just above "SIMPLE OPERATION") doesn't suggest these complications...

http://www.tb-training.co.uk/17Bdomwat.html

It is unusual to have a tap right at the outlet on top of the calorifier. More likely it is the control valve for the thermostatic mixing valve.

 

The point of such valves is that the engine coolant, and hence the water in the calorifier, can be up around 80 deg C or more, which is scaldingly hot. By contrast the hot water system in a house is usually around 55 to 60C. So a thermostatic mixing valve can be fitted which automatically mixes cold water with the very hot, to give hot water around 55C, the exact temperature being dependant on the setting on the thermostat knob (ie possibly, the knob that you think is a “tap”).

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1 hour ago, Njiruk said:

The diagram on this page about domestic water systems (just above "SIMPLE OPERATION") doesn't suggest these complications...

http://www.tb-training.co.uk/17Bdomwat.html

In the system shown on that link the hot water is stored in the calorifier at the same temperature as it comes out of the taps. Use of a blending valve on the calorifier outlet allows hotter water to be stored and blended with cold water to reduce the temperature of the water supplied to the taps. This increases the total amount of stored hot water available and avoids the risk of scalding.

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1 hour ago, AndrewIC said:

Thermostatic mixing valve somewhere to prevent scalding?

That would make sense, thanks!

I noticed irregular behaviour because the hot water I'm getting out of my taps doesn't reach the hot temperatures I could get some months ago. It would be explained if this valve is regulated according to the hot input only, as the cold input is colder now in winter. Too bad though, because sometimes I'd like to get that very hot water that's just there! I can tap it from the calorifier output directly, but still, I'd have preferred simplicity: no thermo mixing valve!

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1 hour ago, David Mack said:

Use of a blending valve on the calorifier outlet allows hotter water to be stored and blended with cold water to reduce the temperature of the water supplied to the taps. This increases the total amount of stored hot water available and avoids the risk of scalding.

Good point, thanks!

It increases the amount of stored hot water available as the 'early mix' avoids a bigger temperature loss that would occur if the hot water were transported directly through the long pipework and mixed to colder at the taps.

Makes sense!

Edited by Njiruk
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1 hour ago, nicknorman said:

It is unusual to have a tap right at the outlet on top of the calorifier. More likely it is the control valve for the thermostatic mixing valve.

It's just a simple inline tap right at the outlet (there is a similar tap at the inlet below). Regulating it may well have an effect on the relative amount of hot water that's mixed in the mixing valve, so in that sense it could be seen as a sort of control valve I guess yes.

The current not-all-that-hot issue I'm describing 2 posts earlier occurs with this tap fully open, sadly.

Edited by Njiruk
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10 minutes ago, Njiruk said:

It's just a simple inline tap right at the outlet (there is a similar tap at the inlet below). Regulating it may well have an effect on the relative amount of hot water that's mixed in the mixing valve, so in that sense it could be seen as a sort of control valve I guess yes.

The current not-all-that-hot issue I'm describing 2 posts earlier occurs with this tap fully open, sadly.

You don’t mention how you heat the water in the calorifier. But really, whatever the method, as you suggest, it needs more energy (longer running if the engine or whatever) to heat water that is starting out at 5C, than it would to heat water that is starting out at 15C.

 

Coming back to the original point I’d suggest spending a bit of time working out which pipes go where, ie draw up a diagram. Then you will have a better chance of working out what’s going on, and it will be easier to fix some future problem. And if you want sound advice from here, a photograph or two is worth a lot of text! 

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Firstly I'm surprised no-one has suggested there should be an expansion vessel on the outlet from your calorifier, to reduces the number of pressure cycles to which your calorifier is subjected and to prevent the pressure relief valve from having to operate. This would cause a litre or three of water to flow from your hot taps after you closed your isolating valve as it discharges its pressure. 

 

Secondly the isolating valve you describe fitted directly to the calorifier outlet should not be there and indicates installation by an amateur or at least by someone who perhaps does not understand plumbing, or who does not see the benefits of installing plumbing in accordance with normal convention. Your calorifier probably has a non-return valve in the water inlet, and with the outlet valve closed there is no provision for expansion so this outlet valve is potentially quite dangerous. Don't ever close it. Or better, remove it. Your system should have a pressure relief valve (PRV) too and this isolator probably isolates it from the PRV. If you must have a hot water isolating valve it should be in the cold water inlet to the calorifier, or if on the outlet, fitted AFTER the PRV and expansion vessel tees. 

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