Set Appliance State:

Ensure No demands are present
Ensure boiler is cool
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Attempt to reset the boiler.
(Control knob to off position then back to DHW & CH position)
Does the boiler reset?
Note:
If after boiler reset the fault code changes from the original to a different fault code, then CLICK HERE.