boiler cycling too often ??

[nudge]

recently my boiler seems to be switching on and off more often than i remember it used to. once the heating water is up to temp the boiler burner shuts down as i would expect but then it starts up again only about 40 seconds later and burns again for around 20 seconds then turns off again then back on 40 secs later etc. i dont remember it cycling that often before and the rads seem hotter than normal. the boiler is a servowarm combi elite 80. is this just my imagination or should it really be on and off so often.

any ideas

thanks neil

 

[oilman]

It shouldn't go on and off so often. The link to the room thermostat is not working correctly andd may be a motorised valve problem (it may be something else of course).

 

[nudge]

thanks for the quick reply. however, we dont have a room thermostat (or a motorized valve) with this system, the only stats are the (non adjustable) contol stat on the output pipe from the burner and the one for the hot water on the output from the heat exchanger. wondering if stat may be faulty but would expect it fail either on or off not to still work over a very narrow band

 

[CH4]

I'm not familiar with your boiler, but if its thermostat is of a bimetal construction, which includes an internal spring to provide hysteresis (a lag between the on and off temperatures), then the stat is the most likely cause of the problem. The springs do break or lose their springiness with repeated temperature cycling. Otherwise, the controller PCB may be faulty.