Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Remove the blue wire from the CH limit thermostat
Remove the blue wire from the CH limit thermostat
Measurement:
Measure the resistance across the exposed terminal and the unexposed terminal (brown wire) of the CH limit thermostat.
Reconnect the blue wire after test.
Reconnect the blue wire after test.
Isolate as per TOPs P4
and refit as necessary