Central heating won't get above aprox 22C

Hello there. Now I am just a boring consumer and no nothing about plumbing etc. I appreciate that it's highly unlikely that a problem can be rectified by someone like me as a result of info posted here but if anyone can give me a pointer or two it will be appreciated.

Soem info:

Boiler:
Ideal Classic FF 350 (G.C. No. 41 391 96)
Thermostat & programmer : Danfoss FP715

This bolier was installed into my new build house in 2002. All has worked flawlessly until the last few days.

I noticed that the house wasn't arming sufficiently in the evening and checked the thermostat. It was on 25C but the thermostat was clicking when rotating the dial to indicate the temp being about 22C and the boiler wasn't kicking in. If I play about with the thermostat and turn it up and down, sometimes the boiler will fire up but just for about a minute. As the temp in the house drops, the bolier will kick in but will only heat up to the 22C and then go off. The HW seems to work fine (ie. we have it!)

Does anyone have an idea as what the problem may be?

Thanks for any advice in advance.

Boiler firing is also controlled by the boilers own internal thermostat which controls the temperature of the water leaving the boiler. You can't have water that is too hot in the radiators it's dangerous.

If the water in the boiler/radiators and pipework are hot it's usual for the boiler to cycle on and off even if the room thermostat is calling for heat. The boiler will just top up the heat of the water to the temperature set on the boiler stat.

When the system is started from cold it will burn longer as it take more heating. The warmer the system and the house are the less the burner will be on.

The boiler is probably working properly. Question is are your radiators as hot as normal?

Hi Stem, thanks for the reply.

That makes sense but I have never had this problem before.

I'v just run a test. I have just come in and the house was fairly cold. Therm was set to about 17C. I turned the thermostat up to 25C and the boiler fired up. The rads got very hot. Good so far. However, as soon as the temp hits 22C the boiler has gone off. The thermostat on the bolier is on max.

What I don't understand is that up until last week and for the 4 years we have been here, I have always been able to crank up the wall thermostat to 25C or more and the boiler would heat the rads until that temperature was reached.

Now, once it gets to 22C the boiler cuts out and then comes on intermittantly as the temp drops below 22C and the rads are only ever luke warm and the house is not warm enough (last night we were cold and the outside temp is a mild 9C!)

i would be testing the roomstat at various temps....sounds like its playing up.

22C seems plenty warm enough - our, calibrated, digital stat normally shows 20 (and is set at 20), plenty warm enough for t-shirts! If you normally have it set at 25C the calibration must surely be out - in which case it could be thinking its 25C and cutting out - even though thermometer is reading 22C.

Assuming you're happy playing around with the electrics - short the stat out and measure the temperature. If the boilder carries on until the temperature exceeds 22C, 25C etc buy a new stat.

P.S. Is the thermometer next to the stat?