Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
DHW Temperature Selector to MAX
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Attempt to reset appliance and allow boiler to
attempt to run then select from options below.
Boiler returns to fault code or does not reset
Boiler runs and ignites - Overheat investigation
(CH Sensor fault can sometimes display due to circulation problems)
Boiler resets but a different fault code appears