Set Appliance State:

Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
Note:
Please ensure that for this test the temperature of the water in the Thermal Store is lower than that at which the Boiler Thermostat will switch in.
To achieve this, switch the appliance off and run a quantity of hot water off.
Remove both wires from the Boiler Thermostat before testing.

Measurement:

Measure a short circuit resistance across the Boiler Thermostat Connections
(test across Thermostat, not the brown wires).
If an open circuit is detected, run off a little more hot water and repeat test.
Note:
Reconnect Boiler Thermostat wires after test.