Thermostat Overheating

[Ashleigh-Kate]

Several times a week our living room thermostat reaches 23/24 making the house uncomfortably hot. Twice we've called an engineer out, the first said it isn't costing us as the boiler isn't "calling for gas" when it overheats (how he knew this I've no idea!) and he failed to do anything. The second engineer blamed the weather and the sun shining through the window!! Unfortunately I was out both times and my partner accepted what they said.

But last night the house had become unbearably hot and on checking the thermostat it was on 26, the radiators were red hot and I immediately went up to turn the boiler off to find it was still going! This told me the thermostat is failing to send a signal to the boiler to switch off when it reaches its set temperature.

When I told my partner this (he'd gone to bed) he know realises the thermostat must be faulty but we are not sure what to do next. What if a third engineer still insists there is not a problem?

 

[steptoe]

is it a wireless stat or wired?

 

[Richard-the-Ninth]

Several times a week our living room thermostat reaches 23/24 making the house uncomfortably hot.

Have you tried turning it down to say 20? 23 is on the hot side. Also is it a mechanical stat or electronic?

 

[NozSpark]

is it a wireless stat or wired?

and is it a programmable stat?

 

[Murdoch]

Many boilers continue to "run" for a couple of minutes AFTER the thermostat has sent the signal to switch off.

Lets hope you are not paying per visit!

 

[Ashleigh-Kate]

Thanks so much for all the replies. In answer to your questions it is wired,electronic and programmable. As for the boiler taking a few minutes to switch off after the thermostat sends a signal it would have taken a lot longer than a few minutes the time I noticed it was still going when the thermostat was showing 26 as the signal should have been sent when it reached 21. Last night the thermostat went to 24.5 and again the boiler was still going. I didn't turn it off as I wanted to see just how high it went but when I came down from having a shower my partner had cooled the room down by opening the back door although it still showed 24.5 until I went to bed and turned it off.

Yes unfortunately we are having to pay each time an engineer comes out which is all the more reason I want the problem solved next time we call one. Today the thermostat has behaved perfectly, never going above 21 so I'm biding my time but I will make sure I am here next time. I still can't believe my partner accepted what the first engineer said about it not costing us - I know very little about central heating but even I know that much heat cannot be generated for free!

 

[steptoe]

is it a combi boiler?

or a system boiler?

it could be a sticking valve if its a system boiler.

 

[ProDave]

If you are paying each time and not getting a resolution, then simply you are getting the wrong person out.

Get a local electrician, but check first that it's one that understands heating systems and controls.

I suspect Steptoe has it right, that a motorised valve is sticking.

First thing for the electrician to check is that the thermostat really is switching on and off at the right temperature. for that he will need a volt meter.  Did your chap use any form of test meter to verify this?

If the thermostat is working, next thing is to determine if it switches the boiler directly or if there is a motorised valve anywhere and test accordingly.

 

[Ashleigh-Kate]

Oops sorry folks I forgot to say it is a combi boiler, only 4 years old. Perhaps I should mention the reason my partner called the second engineer out was because we thought the boiler wasn't going off when we switched it off manually at night as usually it stops almost instantly and when it didn't do this a couple of times we thought it wasn't going to go off so we turned it off at the mains and called the engineer the next day. He told us we need to wait for about a minute for it to go off and he was right. I find this strange as for 4 years we've never had to wait, we turned the dial to off and the boiler stopped within seconds. Anyway while he was here my partner mentioned the thermostat overheating and that's when he blamed the weather and the sun shining in the window! Had I been here I would have told him this was rubbish as it happens mostly in the evening but my partner didn't think of that (well he is 78 and maybe missing a few brain cells lol).

In answer to your question, no neither engineer used a test meter!

 

[Sharpend]

This stat is a digital display- correct? It shows both set temp and actual temp?

Have you had any work carried out recently on the boiler?

Do you have more than one stat?

What area are you?

 

[Ashleigh-Kate]

Yes the thermostat is a digital display. We recently had the boiler serviced but no other work. We just have the one thermostat which is in our living room. We live in Peterborough.

 

[NozSpark]

TBH it sounds like the programmable stat needs re-programming

Do a factory reset on it and start again

 

[Ashleigh-Kate]

Re-program no problem but how do I do the factory reset? It's currently on 22 but I've a feeling its gonna creep up again so if it's possible to explain the reset I'll give it a try, thanks.

 

[NozSpark]

Haven't a clue as we don't know what model the stat is....

You at least need to go through the program and check all its settings

 

[ProDave]

Presumably it has two displays, the set point, often in small digits, and the actual temperature, usually in large digits.  It will also have some form of symbol on the display that lights up when it is "calling for heat"

The important thing is keep an eye on the "call for heat" flag.  the boiler sould only come on when that is on. If it does, then everything is working as it should.

I presume when it runs away and the room gets too hot the call for heat flag is off?

 

[Ashleigh-Kate]

The thermostat is now on 22.5 but the boiler is not going. The little flag you mention is not showing. I assume that's what the first engineer meant when he said it wasn't calling for gas? But it wasn't overheating when he was here so how would he have been able to say it doesn't cost us because it wasn't calling for gas when it does overheat? My partner is now insisting again that it is fine (he saw me checking for the flag) and it seems he still believes it's not costing us when it overheats! But on the occasions when it was showing well above 21 and the boiler was still going surely it was costing?

Sorry I didn't answer your question about the flag but to be honest I can't as I didn't know it existed!

 

[steptoe]

ok, here is a problem with some prog-stats,

once you manually adjust it, it stays on that setting for the rest of the day, it only reverts back to the programme when the next day starts,

so, if you are a bit chilly and set the stat to 26 for a quick boost, it will remain there until midnight before it reverts to the programmed settings.

 

[NozSpark]

Most modern boilers have something called pump overrun. This is to make sure that the heat exchanger and other components aren't damaged by the heat building up so it carrys on circulating the water until it has cooled down sufficiently.

The flue fan can also run under certain circumstances (IIRC), however it shouldn't be using gas unless the programmable stat calls for heat or there is a hot water demand

 

[Ashleigh-Kate]

I have to admit here that I have never adjusted or set the thermostat as my partner has always done it so I have no idea how to reset it but I will ask him to do it (he won't be happy as he is adamant there is nothing wrong with it!). It is currently on 22.5 but there is no flag showing. Can I just confirm that I don't need to press any of the buttons in order to be able to see the flag?

 

[Sharpend]

Can you tell us which make and model if thermostat to have and we could give guidance on how to reset. The flag/indicator should only be present when the temperature has fallen below that of the required room setting and the boiler has lit up.