Set Appliance State:

Set Multimeter to AC Volts Set meter to measure AC Volts
Isolate Mains Power to appliance as per TOPs P4
Gain access to mains in connections.
Disconnect 4 wire connector from the mains in connections and make safe
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Reset appliance.
Has the fault code cleared?