Set Appliance State:

Mains Power Off
CH Demand
Ensure Primary Heat Exchanger is Below 40°C
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Preheat switched OFF (ECO button illuminated)
Does the burner ignite with a CH demand?
Note.
There may be a delay (anti-cycle time) between DHW to a CH demand.