Heating coming on when thermostat is off - heat being wasted!

[PunishmentRoundupWithJoon]

A couple of times over the past few weeks, my heating has come on, despite the thermostat being off. I came home yesterday and as soon as I walked in, my glasses steamed up, so I knew straight away it had happened again!

Is there any reason why this might be happening?

The thermostat is located in the living room and was definitely set to zero. The heating is not, and never has been, on a timer. It's a manual one, a dial that you just set to whatever temperature you require.

I have turned all radiators down today in case it happens again. Not the living room ones though as they don't have the valves.

The thermostat is not the type to take batteries (someone asked me this so am posting here in case that makes a difference.)

I hadn't done anything different to the boiler in the preceding few days before this started to happen.

The boiler is a Worcester 24i Junior.

I am getting an engineer to look at it soon (it's a housing association property) but thought I'd post here in the meantime.

Could it be anything to do with the very cold weather? But surely, even so, if there thermostat is off, it shouldn't kick in?

Any input appreciated!

I think it's probably frost protection, boilers will fire up ifor a short time in cold weather even with the thermostat off .

@Tittyfilarious - Hi, thanks for your reply. Yes, I've heard my boiler do that on occasion, but with this issue, they radiators were full on, blasting out heat, despite thermostat being off. That shouldn't be happening. They had clearly been on some time to, judging by the heat of the house! Particularly annoying as I'd left the windows open to air the place!

What do you mean by 'set to 0', have you got a pic? Some thermostats have a 'come on if the temp gets below ' setting so if that was set to 0 it would come on in that situation?

@PunishmentRoundupWithJoon Ah that does sound like it's something else rather than frost protection then , could be a fault with the thermostat dial .

We had exactly the same problem a few weeks ago

I think where the boiler is something had hit against a setting causing it to happen

we had a new set thermostat and it’s been fine since

@User543211 - don't have a pic at the moment and it would be useless anyway as the thermostat is so old, all the numbers are rubbed off! Apart from the top end, where you can see '30'. When I say set to zero, I mean totally off, as far as it can go to the 'off' side. It doesn't have that setting for coming on at a certain temperature, as I've been in this property for many years and it's not happened before.

Have checked the manual for the boiler online and now turned off the heat setting so will simply turn that on again when heat is required. And someone will come out next week. Could've been today (impressed with housing association) but I have an appointment.

I ended up switching the boiler off for 10 mins and then put it back on and it’s been fine and got a new thermostat

Could be a diverter valve.
We had the same issue when we had hot radiators when they were supposed to be off

Same, a common problem unfortunately.

Could it be that zero is not zero on your thermostat if the numbers have rubbed off? And instead the lowest temp is something like 5 or 10 or 15, and it is dropping below that?

What timer and thermostat are you suing? Are they Hive / in the cloud? Check your settings.
Where is the boiler located, is it in an area that gets cold?

The frost protection is built in to the boiler to protect it, regardless of the room stat setting.

It will be the frost protection on the boiler as others have said. It would be a really expensive error to turn it off much cheaper to just pay for the extra fuel

I doubt it's the frost protection if it's blasting the amount of heat that OP is saying.
I'd get the diverter valves checked though

@Wibble128 - no, nothing that modern! Just an old dial thing on the wall of the living room. Boiler is in the kitchen, probably the warmest room in the house. I don't use a timer. Just switch thermostat on when needed, about four times a day.

@dementedpixie - Hopefully the engineer will be able to sort it next week.

@Autumn1990 - The maintenance team didn't suggest that it was frost protection, and they know the radiators. There is a frost protection setting on all radiators except the living room ones and they are not set to that. There is nothing in the boiler manual about frost protection. And the amount of heat that the radiators were kicking out was phenomenal.

There will be frost protection on the boiler and it will be full heated

@Autumn1990 - you're right, I've just checked the manual again. However, it states that it will up the temperature to 12 degrees - when I came home the temperature was 25 degrees!

A valve could be sticking or your thermostat might not be working properly.

I don't think it's frost protection as it's getting too hot for that.

An engineer should be able to identify the problem quite easily if it's replacement valve or a new thermostat that's needed. Both are fairly standard issues.