Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Summer/Winter Switch set to Summer.
Remove combustion chamber cover.
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

HW tap OFF - fan will be rotating at slow speed.
Turn on HW tap, fan should rotate at full speed.