Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
Turn Hot Water Tap On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the AC voltage between the live and neutral connections at the fan assembly.
Expect mains voltage.
Is the voltage measured as expected?
Note:
Fan appearance may differ but the test remains the same between the live and neutral connections.