Set Appliance State:

Gas Off
Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
Unplug connector CN4

Measurement:

Measure resistance across CH Thermistor (purple wires).
This should be in the range 2 kOhms (Hot) to 13 kOhms (Cold).
Replace connector CN4.
Note:
This test should be carried out on the
disconnected connector, not on the PCB.