Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove fan assembly (take care as appliance maybe very hot)
Disconnect leads to condensate sensor
Unscrew one side of the cable element from a terminal

Measurement:

Measure for resistance across the two exposed terminals of the condensate sensor.
Although the condensate resistor is not a thermistor it does still have a
negative temperature coefficient, as a result when the appliance combustion
chamber is warmer the resistance measured will be lower and vice versa.
Expect a resistance between 170 kOhms and 400 kOhms.
The resistance measured should lie between these values,
relative to the appliance combustion chamber temperature.
Is resistance measured as expected?