I have a worcester 24i junior condensing boiler and everything has been great for the past 18 months, then suddenly the boiler has started to come on at odd times when the timer has not been programed to come on at that time, can anyone help me

kay fitzpatrick, February 2009

sure this boiler has a facility for preheating dhw could be that check to see if it has been turned on

bss, February 2009

Some installations have a frost-stat intended to stop the pipework freezing up. This chap bypasses all other controls. It may be asking the boiler to come on because of low temperature or it might be faulty. They are usually placed in cold parts of the house like an unheated garage.

Peccavi, February 2009