Set Appliance State:
Gas On; Pilot On
Set Multimeter to mVolts DC 
Isolate Mains Power to appliance as per TOPs P4
Selector Switch OFF
Gas Control Knob in Pilot Ignition position
Attach crocodile clip to Boiler Overheat Cut Off
Selector Switch OFF
Gas Control Knob in Pilot Ignition position
Attach crocodile clip to Boiler Overheat Cut Off
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Measure voltage across LOWER terminal of Boiler Overheat Cu tOff and Gas Valve body, whilst keeping Gas Control Knob depressed.
Voltage measured should be greater than 8mV DC.
Voltage measured should be greater than 8mV DC.
Isolate as per TOPs P4
and refit as necessary