Following the manufacturers fault finding manual everything pointed to the PCB being at fault, this has been replaced but the boiler still will not reset.
The pump is running and so is the fan. The temperature sensor checks out approx 11k ohms when cold - reduces to approx 4k ohms when put into hot water. The overheat thermostat has not tripped out.
The system pressure is 1 bar and the micro switches all check out. Electrically, i am getting the correct voltage to PCB. M1 terminals but no voltage to PCB M4 gas valve and igniter. The reset switch also checks out ok.

Tony, March 2009