Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Ensure boiler is cool
Reset overheat by pushing in red button
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Run DHW tap.
Does boiler reset and start ignition sequence?
Or does fault code flash straight up?
BOILER RESETS
BOILER DOES NOT RESET