Set Appliance State:
Mains Power Off
Set Multimeter to Resistance 
CH Demand
Gas On
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Allow fan to run and system to heat to above 60 degrees C.
Remove brown and yellow wires from CH sensor.
Measure resistance of sensor, resistance should be below 2.5 kOhms.
Note:
To reduce the time taken for the central heating to reach temperature, it may be necessary to reduce the heating load by turning off some radiators.
| Isolate Mains Power to appliance as per TOP's P4 |
Remove brown and yellow wires from CH sensor.
Measure resistance of sensor, resistance should be below 2.5 kOhms.
Note:
To reduce the time taken for the central heating to reach temperature, it may be necessary to reduce the heating load by turning off some radiators.
Isolate as per TOPs P4
and refit as necessary