Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Ensure that the Boiler has been running and that the Boiler is at a reasonable operating temperature.
Ensure that the Boiler has been running and that the Boiler is at a reasonable operating temperature.
Measurement:
Turn the Thermostat down to its minimum setting.
Remove both the Red/White and the Pink spaded wires from the Thermostat and measure the resistance across the two spade terminals on the Thermostat.
Reconnect wires after test is completed.
Remove both the Red/White and the Pink spaded wires from the Thermostat and measure the resistance across the two spade terminals on the Thermostat.
Reconnect wires after test is completed.
Isolate as per TOPs P4
and refit as necessary