Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect sensor plug from the PCB (CN14)

Measurement:

Measure resistance across the blue and white wires on
the left side of plug CN14.
The resistance measured will depend on the boiler temperature but should conform to the table below.
Temp °CResistance in kOhms
20 - 308 to 16
30 - 40 6 to 10
40 - 503.9 to 8
50 - 602.5 to 5.5
60 - 701.5 to 3.0