Set Appliance State:

Mains Power Off
Turn Hot Water Tap On
Selector switch to Off position
CH temperature selector to Max
DHW temperature selector to Max
External controls not calling for heat
(if external controls are not fitted then remove link between terminals 3 & 4 on main terminal block)
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Selector switch to DHW and CH position
Observe boiler. Does the boiler attempt to run?
Note:
The appliance has built in frost protection so that should the system temperature fall below 5 Deg C, the boiler will fire on its minimum setting until the flow temperature reaches 30 degrees C. The boiler firing under these conditions should be considered normal operation.