Set Appliance State:

Mains Power Off
Gas Off
Set Multimeter to mVolts DC Set meter to measure DC mVolts
Turn Hot Water Tap On
Rotary Switch to DHW position
Hold in Boiler Casing Switch
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

With Pilot alight (hold in Gas Control Valve) measure between Boiler Casing and BOTH Red wires of Pilot Off button.

Voltage measured should be greater than 8mV DC.