Set Appliance State:
Gas Off
Set Multimeter to AC Voltage 
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Selector switch to HOT WATER position
Gain access to PCB (use insulation mat as necessary)
Selector switch to HOT WATER position
Gain access to PCB (use insulation mat as necessary)
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Depress the gas control knob. Allow the boiler to execute its purge delay period and measure the voltage across connection 55 (blue wire) and connection 56 brown wire at connector D on the PCB.
Note:
Gas control knob should be fully depressed while measurement is being taken.
Note:
Gas control knob should be fully depressed while measurement is being taken.
Isolate as per TOPs P4
and refit as necessary