Set Appliance State:

Mains Power Off
Gas Off
Set Multimeter to DC Volts Set meter to measure DC Volts
Selector Switch to HW & CH position.
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure Voltage across connector M11 connection 52
(Red wire) and connection 47 (Black wire) on the main PCB.