Set Appliance State:

Set Multimeter to Resistance Set meter to measure resistance
CH Demand
Isolate Mains Power to appliance as per TOPs P4
Selector switch in winter position
Timer switched to FIX ON
Remove plug J12
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure resistance across black wires of plug J12.
Note:
Do not take measurement on PCB.