Set Appliance State:

Mains Power Off
Ensure NO Demands
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset the appliance (press and hold reset button for 5 seconds).
Does the fault code reset allowing further investigation or is the appliance stuck in the fault code?
BOILER RESETS - (RETEST APPLIANCE)
BOILER WILL NOT RESET - (STUCK IN FAULT CODE)