called to see to a csi 85t boiler with no ch or hw boiler would come on as you looked at it with out doing anything at all to it then it wont work at all book says to look at main switch then points you to the pcb board there is 240 volts at the incoming mains at the board connections as nothing is running at all like the pump fan theres a thermistor stat on the ch side with two yellow wires to it this stat has to work for the boiler to begin the start up mode if it packs up it gives the symtoms of exspensive repair when the the stat is only a few quid an easy to replace you have to start somewere as they say
ray hughes local council plumber, April 2009