Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove the Brown wire and the Blue wire from the HW Sensor
Measurement:
Measure the Resistance across the terminals on the Sensor.
The resistance measured will depend on boiler temperature and should lie between 500 ohms and 1500 ohms, the cooler the water the lower the resistance. For boiler to operate at full gas rate resistance should be between 500 ohms and 1000 ohms.
Replace leads after test.
Note: If this test has been called after failing burner modulation and the water is 60 deg C the resistance should be approximately 1000 ohms. The Sensor will cool quickly if the DHW tap is left on.
The resistance measured will depend on boiler temperature and should lie between 500 ohms and 1500 ohms, the cooler the water the lower the resistance. For boiler to operate at full gas rate resistance should be between 500 ohms and 1000 ohms.
Replace leads after test.
Note: If this test has been called after failing burner modulation and the water is 60 deg C the resistance should be approximately 1000 ohms. The Sensor will cool quickly if the DHW tap is left on.
Isolate as per TOPs P4
and refit as necessary