Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
No demands present
Gain access to terminal block
Remove external controls connected to
terminals 1 & 2 and make safe
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Cancel boiler purge / self-check (reset) if required.
With external controls disconnected does the boiler still attempt to run for CH (radiator symbol displayed)?