Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to DC Volts Set meter to measure DC Volts
CH Demand
Gain access to PCB (use Insulation Mat as required)
Main On/Off Control in the On position
Heating Control to Heating & Hot Water
CH Temperature Control to Maximum
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

If a fault code is displayed press boiler 'Reset' button.
Measure DC Voltage on across X49 on Motherboard.
This should lie between 20.0 and 30.0 V DC.