Hot Water Thermostat problem

[Barretec]

Hi,
Noticed the boiler was running for long periods during summer, checked motorised valve, working OK, cylinder thermostat working when water goes cool, however, it seems the thermostat will not switch off at the required temp.

What I have tried

Ran the bath to empty the hot water

Set the cylinder thermostat to 50.
Boiler kicks in and runs for 4 hours.

Turned the cylinder thermostat down until it clicks and cuts out the boiler, but then the cylinder thermostat won't click on until it hits 65 (full on).

The boiler does eventually go off so the thermostat must work at some point.

The hot water is always ON at the controls and has been since we moved into the new house 3 years ago.

Is there a better way to check the thermostat please.

 

[Armo74]

Cylinder thermostat should be set at 60-65.
Is the boiler thermostat turned down?

 

[Barretec]

Thanks for the reply.

Boiler control set at 4.5 out of 6.

Water temp from tap very hot

The cylinder thermostat is normally at 60 I moved it to 50 for the test I did to see if the cylinder thermostat would switch off as it reached 50.

 

[Barretec]

I just re read my original post, to clarify this sentence.

"Turned the cylinder thermostat down until it clicks and cuts out the boiler, but then the cylinder thermostat won't click on until it hits 65 (full on)'.

after turning the cylinder thermostat down to cut out the boiler, if I then immediately turn the thermostat up it won't click until it hits full on, that makes me assume the water in the tank is at 65 even though the thermostat was at 50.

Hope that makes more sense

 

[jeff the gasman]

Put a new stat on and make sure the boiler stat is set higher than the 55 degrees you set your new cylinder stat to.
The diverter valve is irrelevant when hot water only is selected.
Jeff

 

[Barretec]

Hi Jeff
So you think the stat is bust, It's certainly not working correctly was my take on it. Just wondered if there was a way of checking is was bust.

Having looked on the internet I see the replacement varies from £20 on ebay to over £100 which is a bit of a swing.

Do you have any thoughts on that before I order one.

see current stat

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• Barretec
• 30 Aug 2014
• 1

Untitled

• Barretec
• 30 Aug 2014
• 1

 

[ChrisR]

So from the look of it, you have an Unvented (mains) hot water cylinder, or a heat store, or something other than a plain old HW cylinder?

If it's low on the cylinder, 55º will be plenty, the water at the top will get hotter.
Yes they're expensive. Only way you can test it would be to remove it and test in a water bath with a thermometer...
The hysteresis shouldn't be more than 10º or so.

 

[Barretec]

Update on my problem, Ordered a new thermostat from ebay, installed in about 15 minutes, works a treat.

Interestingly, In most houses I've owned have always let the hot water be controlled by the thermostat as opposed to the clock program, makes me wonder if this is the best practice as this problem has at least doubled my gas bill through the summer.

It was only because I'm now retired and the need to conserve costs that I noticed the boiler being on.

So, a couple of questions.
1. Is it best to control the hot water via the clock or by the thermostat.
2. Is a faulty thermostat a common occurrence.