Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to DC Volts 
Turn Hot Water Tap On
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Once the fan begins to run measure the DC voltage between the black wire on plug X23 at the PCB and a suitable earth point.
Voltage should be approximately 5.5V DC.
Voltage should be approximately 5.5V DC.
Isolate as per TOPs P4
and refit as necessary