Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
CH Demand
Selector switch set to CH position
Boiler CH thermostat set to MAX
Ensure CH controls are calling for heat
Clock switched ON
Remove connector CN1 from the PCB

Measurement:

Measure the resistance between pin 4 (black)
and pin 5 (black) on connector CN1.