Thermostat not turning heating off

Hello experts...

My thermostat is at the lowest setting (10 degress) but the heating is on continuously. The boiler is set to automatic so it should run off the thermostat. All other settings work fine (eg the timer times the heating properly and it turns on and off fine..), The thermostat still 'clicks' when turned up and down which suggests it is registering the correct temperature (clicks at around 20 degrees).

any thoughts?

more info reg,is it a combi? y plan, s plan etc

Could be a frost stat turning it on. Without more info we cant help you any more than that

It is a gravity fed system with the boiler in the kitchen (ground floor) and a hot water tank in the bathroom (1st floor). There is a thermostat in the hallway on the ground floor and a panel in the kitchen that you can (or should be able to) control the timing of the heating with and turn the heationg and hot water on and off.

I may have been slightly mistaken above - it seems that the heating won't turn off at all no matter what I do to the thermostat or control panel!!!???

Any help much appreciated - its getting seriously hot in the house...!

I guess I could just turn the rads off but spent ages fine tuning them for perfect heat around the house so reluctant to fiddle with them....

Not something silly like you've pressed the CH override button on the prog ? Failing that, for the sake of a few quid, change the therm, just remember its mains 230v in there. If you do that, whilst you have it disconnected (and with the wires well separated) fire the boiler up again and the CH shouldn't come on. If it does, there is a problem elsewhere.

no I checked that...pressing the override button makes the red light go on and off on the progammer but does not seem to affect the heating..

Will try your suggestion and report back..thanks

Before buying replacement, just disconnect it first and try again. Don't forget that its mains voltage in there.

will do - if you don't hear back then say a prayer for me!

When a stat clicks that is usually the sound of a contact making or breaking so to me it sort of rules that out to a point. The fact that the programmer wont turn it off suggests to me that he programmer is cream crackered or perhaps another wiring fault
You still haven't told us the make and model of your boiler.
You say that the system is gravity fed but not whether you have a gravity primary hot water circuit or the system is fully pumped.
What make and model programmer is it?
Do you have a diverter valve?
Do you have a cylinder stat?

The big question you should keep in your mind when looking for this fault is :- Where is the boiler picking up the live from for it to not turn off?

Not sure if the thermostats you have there are similar to those we have here, but...

the ones we have here have a "heat anticipator" built right into them.

The heat anticipator is nothing more than a small electric heater that warms the bi-metallic coil in the thermostat, thereby fooling it into thinking that the room is warmer than it really is so that the thermostat shuts the heat off before the actual temperature setting on the dial is reached.

And, the reason why you need that is because normally the radiators or warm air registers will be located around the perimeter of the house, whereas the thermostat will be centrally located.

So, if the heat from the radiators or warm air registers warms the air in the house from the perimeter inward, then by the time the temperature at the centrally located thermostat reaches the set temperature, then the air everywhere else in the house will be warmer than that.

Also, with hot water heating systems, if the thermostat only shuts the heat off once the air temperature at the thermostat reaches the set temperature, then the temperature in the room will overshoot that set temperature because the hot heavy cast iron radiators will continue convecting heat into the room for a long time after the thermostat is satisfied.

For both of those reasons, you need to fool the thermostat into shutting the heating system down prematurely to avoid overshooting the set temperature, and the heat anticipator does that by electrically heating the bimetallic spring.

I'm wondering if the problem is that the heat anticipator setting in your thermostat is set very low that it's not heating the bimetallic spring enough, and the temperature in your house is overshooting the thermostat setting as a result. (?)

That sounds like a plausible explanation...thank you.

I managed to get some more information last night so see what you think of this:

I went to work yesterday and in the morning turned the heating off manually by physically sliding the switch on the programmer to off. (I have a sliding switch for the heating and the hot water and the usual override 'buttons' etc).

When i came home the heating was still on!? What I then did (or to be fair my better half did), was to flick the HOT WATER sliding switch on and off a few times (it had been on the whole time), and left it in the on position. This, strangely enough, resulted in the HEATING turning off. Throughout this period the thermostat has been on the lowest setting.

I then set both heating and hot water to timed, coming on early the next morning. When i woke up the hot water appeared to be working but not the heating, suggesting that the automatic switch on and off does not seem to work...

I then tried the trick of the previous night to try and get the heating back on, sliding both the heating and hot water switches backwards and forwards, leaving them both in the 'continuously on' position. This did not work. Neither did hitting the override button or 'extra hour' button.

I then realised that the thermostat was still in the lowest possible setting, so I set it higher (higher than the point where it makes that clicking noise), and repeated the above. This time the heating came on. I suspect that when I go home tonight that it will still be on no matter how hot the house is.

So, in summary, the hot water seems to switch on and off fine. The heating does not switch on or off unless the hot water sliding button is slid backwards and forwards a bit, and it seems to be sensitive to the thermostat position, even when set to continuous, which I would have thought should ignore the thermostat as we also have a setting called automatic....It seems like the automatic heating on and off is broken, but some sort of manual intervention helps...

Hope you can make some sense of this, got a feeling the programmer is simply *&$%!ered.

Thanks for your help so far...much appreciated.

Slugbabydotcom said:

You still haven't told us the make and model of your boiler.
You say that the system is gravity fed but not whether you have a gravity primary hot water circuit or the system is fully pumped.
What make and model programmer is it?

Do you have a diverter valve?
Do you have a cylinder stat?

The big question you should keep in your mind when looking for this fault is :- Where is the boiler picking up the live from for it to not turn off?

Click to expand...

In answer to the above - The programmer is a honeywell, don't know the model number. Can look tonight. Not sure what you mean by the other questions. There is a separate hot water tank for the hot water with a separate gravity fed heating system. Don't know what a diverter valve or cylinder stat are sorry..!

You need to find out what the thermostat actually controls. It WON'T be the boiler, directly. My guess would be that there is a three-port motorised valve which is stuck, so that whenever you try to heat the water, some of the heat gets to the radiators too.

I'm afraid the long answer about the anticipator in your thermostat is a complete Red Herring - working or not working would only have a marginal effect.

croydoncorgi said:

My guess would be that there is a three-port motorised valve which is stuck

Click to expand...

Was always gonna be that really wasn't it? anticipator? heh heh

the thing is that I can have hot water and not heating....

the thermostat does seem to have some sort of effect on the programmer (which is separate from the boiler), in that the heating will not come on unless the thermostat is on high enough. It just won't turn off properly, without the ridiculous playing around described above.

It seems to me that there must be some sort of short/bad connection/faulty switch in the programmer so that when the heating is on and the thermostat tries to turn off, that the programmer for some reason does not follow suit? Make any sense?

Currently the heating is on and the thermostat is at its lowest setting. If i go and turn the heating off at the programmer it will stay on, but if i fiddle with the hot water switch by sliding it back and forwards the heating will turn off.

If you tell me what this valve looks like and where I might find it I can have a look.....