Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to DC Volts Set meter to measure DC Volts
Turn Hot Water Tap On
Remove fan connector and make safe
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Reset the appliance.
(Press reset button once then release)
Measure the DC voltage between pin 1 on connector CN4 on the PCB to a suitable earth point.
DC voltage should drop to approximately 55 Vdc.