Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to DC Volts 
Gain access to PCB (use insulation mat as necessary)
Gas On
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Turn on hot water demand
Measure voltage between brown (3) and earth at X401.
Expect approx. 33 VDC.
This is the DC supply to the fan.
Measure voltage between brown (3) and earth at X401.
Expect approx. 33 VDC.
This is the DC supply to the fan.
Isolate as per TOPs P4
and refit as necessary