Set Appliance State:

Mains Power Off
CH Demand
CH Temperature Control to MAX
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance as necessary.
Allow the boiler to attempt ignition sequence, does the fault occur during a CH demand?
Reset appliance (if necessary)
Turn hot water tap ON.
Does the fault also occur during a HW demand?
If the fault does not occur on either demand (fault is intermittent) select that option below.