boiler works fine in dhw mode but will not fire in ch. it will run the pump and fan and pressure switch and divert on the hydraulic valve and make the microswitch for ch. there is voltage 20 v at the switch, so the next sequence is for ignition but will not fire. all tests ( ntc, overheat stats have been checked) have been carried out as per manufacture.

dennis, November 2006

make sure the diverter valve on the right hand side is pulled fully inwards and both microswitches on it are made. If so, the servo valve is not in hot water mode. Next the fan should run and air pressure switch should make so long as the boiler isn't up to temperature or in time delay mode (air pressure switch can be linked out to prove it) If this is all ok, due to the fault only being apparent on heating, it is most probably a PCB problem. The real problem lies it deciding which PCB! In this case i would go for the thermostat PCB or the mother board. If only changing one of these PCBs you will need to know if it is a hybrid model or not. Remove the knob from the thermostat and if the spindle is white it is hybrid, if it's anything else it is non hybrid. If changing both PCBs as a pair, this doesn't matter. Good luck!

Andy, heating engineer., December 2006

checked that it appears to be pulled right back thus leaving the microswitch in the open circuit position.denni

dennis, November 2006

There is a little cam that operates a switch on the water section (this behind the water temp dial). The cam is pushed by a pushrod from the water section. Make sure that the cam is in the HW position (pulled back by spring).

John, November 2006