Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Disconnect inline connector for detection electrode, bottom left of combustion chamber
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Cancel purge cycle & reset boiler (see note).
Does the boiler reset?
Note:
1. For guidance on cancelling purge cycle CLICK HERE.
2. To reset boiler, turn CH temperature / function control to the standby position & return to max.
3. If after boiler reset the fault code changes from the original to a different fault code, then CLICK HERE.