Set Appliance State:

Mains Power Off
DHW demand from programmer
DHW temperature selector to high setting
Ensure hot water storage vessel is calling for heat
CH temperature selector to Off position
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Boiler On/Off switch On.
Reset lockout if necessary.
Does the combustion fan start to run?