Central heating thermostat problem.

[jeannamacs]

My OH broke our (vrt 30 vaillant) room thermostat at the beginning of the summer, by forcing it beyond the off mark at 5 degrees. The mark at where the heating switched on seemed to have altered and it was stuck at 30 degrees and roasting hot radiators. Consequently i switched the heating off for the summer. We have just bought a new thermostat and fitted it, now it is not coming on /igniting the boiler until the 20 degree mark and the radiators are still roasting hot. The small booklet with the instructions says nothing to help us.
Does anybody know if we can we adjust this or will we need to get an engineer/electrician? Were lost and really cant afford a big repair billl at the moment. Hope someone can help.

[The Builder]

Should be a simple, direct replacement, Jean. What's the make and model of the broken one?

[Ankou]

you can buy them for £11 - £15 new. so as said, should be fairly simple.

[ChuckFickens]

I'm not sure I understand the problem though...

"now it is not coming on /igniting the boiler until the 20 degree mark"

That sounds about right seeing as it's not that cold at the moment, so I wouldn't expect the thermostat to switch the heating on until you set it above about 20degrees (i.e. above the current room temperature).

"the radiators are still roasting hot"

Well they would be if the thermostat is set high enough to make the heating come on. the room thermostat doesn't control the temperature of the rads, that will either be set overall by an adjustment on the boiler, all the room thermostat controls is what temperature the heating turns on and off.

[redcrx]

are you sure its the thermostat and not the pump? ours sticks meaning that radiators come on whenever the hot water is on

[jeannamacs]

Thanks for the replies,
"Chuckfickens" someone told us today exactly what you said. and I understand that principal. but before this it was always possible to have the heating on set between 15 and 20 degrees. what is happening is if we set it at 20(the position where I hear the click) It is far too hot and when we lower it, it just goes off. I have lowered the dial on the boiler to the middle setting for the radiators which the manual states should be acceptable for this time of year. surely if the room is cold and we just want to warm it up, not roast, the radiators should heat up at 15 -20 degrees. sorry if this sounds stupid, but there's no other way to explain it.
"The Builder" - it is a vrt30 vaillant thermostat, apparently similar to a Honeywell. Thanks again.

[The Builder]

Further to what Chuckles and the others have said .............. firstly, are you talking about your roomstat? The one on the wall, separate from the boiler.

That only controls the circulating pump, not the boiler directly. When it senses eg 20 degrees or below, it starts the pump. The water in the rads is now pumped to the boiler which senses the low temp. and fires up.

The VRT30 is listed as the boiler control........... built in to the boiler for timings, clock etc.

Assuming everything's ok ....... rad temp is controlled by the TRVs (thermostatic control valve) on one end of each rad.
Perhaps you don't have TRVs? That would mean overhot rads because they have no proper control.
Even if you have them ......... one rad (often near the roomstat) must NOT have one for technical reasons...... perhaps that's the one that's too hot. It's kind of meant to be hot.