Set Appliance State:

Ensure heat store is cool
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Turn On a hot water tap and allow boiler to operate for a few minutes
to create a preheat demand, turn tap Off.
Switch preheat ON (ECO button not illuminated)
Allow the boiler to ignite and run for preheat (heat store) operation.
Observe the flow temperature, t will alternate with flow temperature in display. At approximately 65 - 68°C flow temperature, the boiler should shut down, heat store temperature reached, without D6 fault code occurring.