Hot water suddenly lukewarm

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Hello folks -

Until a couple of months ago, we'd always had decent hot water for baths etc.

Our setup is a thermal store with a heat exchanger, heating mains cold water. There's a thermostatic mixing valve, with hot water from the heat exchanger coming into the top of the valve, the mains cold into the bottom and the mixed water out the side into the hot water pipework.

The mixing valve is set to MAX (which presumably means max temperature it will permit).

For some reason, our bath water etc is now only lukewarm despite nothing obvious having changed. We have a solar panel feeding into the tank, which has an LCD display, and the display is showing that the internal tank temperature is as high as it's ever been, so it seems the issue is not with heating the thermal store water.

One thing to note is that I cannot seem to turn the mixing valve in any direction, although as mentioned nothing has changed recently so I have no reason to suspect this setting has changed anyway. Tonight I also noticed that the system pressure was below 0.5bar, so I topped it up to 1.5bar as recommended online.

If the thermal store is at the usual temperature, can anyone suggest why the HW is no longer as hot as it was, and now only lukewarm? Has the mixing valve gone faulty and is letting in too much mains cold?

Any advice would be gratefully received by this novice!
 
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It is possible the blending valve is faulty, the other likely candidate is the plate heat exchanger.
 
How old is the system what is the make and model.

What is the temp of the thermal store?

It could be a few things, possible limescale coating the mixing valve and heat exchanger. Incoming mains colder since summer is apparently over.


Pete
 
It is possible the blending valve is faulty, the other likely candidate is the plate heat exchanger.

Thanks Mick.

The 'out' pipe from the heat exchanger is too hot to touch, so I assume that is fine. If I touch the HW pipe after the mixing valve has done it's bit, it's easier to hold as the temperature is lower (I guess it should be lower, but I suspect I still shouldn't be able to comfortably hold it)?
 
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How old is the system what is the make and model.

What is the temp of the thermal store?

It could be a few things, possible limescale coating the mixing valve and heat exchanger. Incoming mains colder since summer is apparently over.


Pete

Temp of the store is 60 degrees.

Store is a 450L thermal store made by http://www.heatweb.com/ but can't see a model number.

It's been in since 2008/9 or so, and we've never had seasonal issues with water temperature.
 
I would say 60 is not hot enough for a thermal store, although your issue appears to be the blending valve.
 
Depending on whatever model you have 60 degrees is low as most stores operate at 70 degrees and higher.

Has it always been 60 degrees?

Pete
 
Those blending valves have an alcohol or wax element which moves a plunger which controls the amount of hot water it passes.

They usually get seized up by limescale.

Its often quite easy to boil them in sulphonic acid or carefully use 5-10% of HCl cold to dissolve the lime scale.

But most just replace them as they are only about £35.

Tony
 

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