Hot water control

21 Mar 2006
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United Kingdom

My hot water tank has a thermostat, set below 40°C, but the water is much hotter - almost burning to the touch. Any suggestions why?
The thermostat appears to work - both the boiler and valve activate with the "click" of the thermostat, and the click is at a higher temperature (around 60-70°C).
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If you've got a three-way valve, then I expect it isn't cutting off the hot supply from the boiler when the cylinder temperature reaches the setting.

Likely worn out. Might be the thermostat or the emotorised head, though.
You might get an idea by feeling how hot the pipes are round the valve and the cylinder.

Unles your house feels cold, you could turn down the boiler temp until you get it fixed.
It is a 2 way valve (with another on the heating system). I guess it could be passing through though. Worth checking.
Is the thermostat 1/3 of the cylinder height from the bottom?

Is it making good contact with the cylinder?
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Without measuring it, it is about 1/3 of the way up. It appears to be measuring the temperature ok - the click is at a higher temprtature than is set on the dial.
Try winding the dial down to a lower temperature.
JohnD said:
Try winding the dial down to a lower temperature.
Don't do this. 60°C is not a random number - it's recommended as the right comprimise between allowing bacterial growth and being too hot to be healthy.

If the water is too hot then something is faulty and should be fixed. Likely candidates have already been given. If you select CH only and wait for a while, the pipe between MZV and cylinder inlet (usually, but not always, the hgher pipe), should get distinctly touchable, as opposed to being at !ouch! temperature.
The thermostat is already at 40°C - it doesn't go much lower. :confused: The boiler dial is set at 2

When I turn it up to hear the click and teh boiler/valve, it is only for a few seconds so that wouldn't heat the water that hot. Could the boiler water be getting past the valve somehow?

I'm not going to check it at this time of night, but checking the temperature of the pipes around the valves seems a good starting point. Thanks
Softus said:
Don't do this.

:oops: I had in mind that the thermostat might be out of calibration, so that the dial might be set at 60 but it might actually be switching at 70 (or whatever)

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