Set Appliance State:
Gas On; Pilot On
Set Multimeter to AC Volts 
Isolate Mains Power to appliance as per TOPs P4
Boiler ON
Selector Lever RIGHT - CH/HW Position
Room stat calling for heat
Gain access to PCB (use insulation mat as necessary)
Boiler ON
Selector Lever RIGHT - CH/HW Position
Room stat calling for heat
Gain access to PCB (use insulation mat as necessary)
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Toggle the override button on the clock display panel whilst measuring
voltage between A12 (Neutral) and A10 (Live), PCB, track-side, middle right.
Press Override, display shows ON - Mains voltage present.
Press Override, display shows INT - Mains voltage absent.
voltage between A12 (Neutral) and A10 (Live), PCB, track-side, middle right.
Press Override, display shows ON - Mains voltage present.
Press Override, display shows INT - Mains voltage absent.
Isolate as per TOPs P4
and refit as necessary