Set Appliance State:

Ensure there is no demand for either CH or DHW
Selector switch set to ON
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

When power is switched on the boiler the fan will run (for a total of 4min).
With no request for any form of heating the display will show 0
indicating the boiler is in standby awaiting a request for heat.