Set Appliance State:

Mains Power Off
CH Demand
Preheat OFF
Selector switch to Heating and Hot Water position
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

After self check has completed the display should show "c" indicating it has reacted to the heating demand.
Does the boiler react to a heating demand?