Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Ensure that the boiler has not reached its low operating mode temperature
Ensure that the boiler has not reached its low operating mode temperature
Measurement:
Disconnect the White spaded wire and the Yellow spaded wire from the Low Thermostat (1)
Measure the resistance across the Thermostat.
Measure the resistance across the Thermostat.
Isolate as per TOPs P4
and refit as necessary