Set Appliance State:
Gas Off
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Disconnect red wires from Primary Sensor
Measurement:
Measure resistance across the exposed terminals of the Sensor. Resistance should be less than 21 kOhms.
Reconnect wires after test.
Note: Resistance measured will vary according to the Boiler temperature. The colder the Boiler the higher the resistance. If the Boiler temperature is above 9 degrees C, then Frost Protection should not be activated.
Reconnect wires after test.
Note: Resistance measured will vary according to the Boiler temperature. The colder the Boiler the higher the resistance. If the Boiler temperature is above 9 degrees C, then Frost Protection should not be activated.
Isolate as per TOPs P4
and refit as necessary