Set Appliance State:
Mains Power Off
Set Multimeter to AC Volts 
CH Demand
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Reset boiler as necessary.
After allowing at least 15 seconds to elapse after mains power has been switched on to the appliance, measure the voltage across the fan terminals.
Is a constant mains voltage (approximately 230 volts AC) present at the fan?
After allowing at least 15 seconds to elapse after mains power has been switched on to the appliance, measure the voltage across the fan terminals.
Is a constant mains voltage (approximately 230 volts AC) present at the fan?
Isolate as per TOPs P4
and refit as necessary