Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to mVolts DC 
Measurement:
Disconnect the thermocouple wire from the pilot valve and attach the red lead from the multimeter to the thermocouple wire inner sheath.
Attach the multimeter black lead to the boiler chassis.
Depress and hold in the green gas control knob while operating the piezo igniter and ignite the pilot.
Keep the gas control knob depressed and measure the voltage from the thermocouple.
Attach the multimeter black lead to the boiler chassis.
Depress and hold in the green gas control knob while operating the piezo igniter and ignite the pilot.
Keep the gas control knob depressed and measure the voltage from the thermocouple.
Isolate as per TOPs P4
and refit as necessary