Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
DHW 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:

Measure the AC volts at the fan on the plug X7 on the PCB from the live to neutral.
Expected voltage should be between 160v and 240v.
Note:
Ensure a good connection is made.