Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Remove the wires or link from terminals 5 and 6 to the external controls
(right hand side of terminal block, refer to pictures)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the boiler still try to fire for a CH demand?