Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Disconnect the internal programmer to the right of the display board
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the boiler now recognise the demand?
Note:
If there is no internal programmer fitted this test should be skipped.
(select boiler does not recognise demand or no integral programmer)