Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
Gain access to PCB (use Insulation Mat as required)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Reset appliance as necessary.
Allow burner to light and establish.
Measure the voltage between pins 2 and 3
(brown and blue wires) on X6b connector at the PCB.
Mains voltage expected.
Note:
If a white board is fitted connector is in same location but is called X6 instead of X6b.