Set Appliance State:
Set Multimeter to AC Volts 
Isolate Mains Power to appliance as per TOPs P4
Remove connector from the fan and make safe
DHW Demand - Ensure Store is not up to Temperature
Remove connector from the fan and make safe
DHW Demand - Ensure Store is not up to Temperature
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Measure the AC voltage between the blue wire to the fan and a suitable earth point
Voltage should now be approximately 130V AC.
Voltage should now be approximately 130V AC.
Isolate as per TOPs P4
and refit as necessary