Set Appliance State:

Allow pre heat to satisfy
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Fully shut off all the taps in the house and check that none are dripping. Also check that any mixer taps are not passing.
Apply a CH demand.
Once 90 seconds has elapsed & preheat is satisfied, does the boiler return to CH demand mode (c in display) or does it stay in preheat mode (d or t in display)?