Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Ensure the Boiler has been in operation and has reached its mid operating temperature
Measurement:
Disconnect the Yellow spaded wire (connection 3) and the White spaded wire (connection 6) from the Control Thermostat and measure the resistance between connections 3 and 6 on the Thermostat.
Do not turn the Thermostat fully down (Off position), but adjust the Thermostat between its fully high position and its low position. The resistance measured should show the Thermostat to be open circuit in its low position and short circuit in its fully high position.
Note.
Heating load can be reduced by turning off some radiators to reduce time required for test.
Do not turn the Thermostat fully down (Off position), but adjust the Thermostat between its fully high position and its low position. The resistance measured should show the Thermostat to be open circuit in its low position and short circuit in its fully high position.
Note.
Heating load can be reduced by turning off some radiators to reduce time required for test.
Isolate as per TOPs P4
and refit as necessary