Set Appliance State:
Mains Power Off
Set Multimeter to Resistance 
DHW Demand
Gas On
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Run the appliance until the burner shuts down
Disconnect the connector to the overheat stat and gas valve
Measure the resistance between the two red wires.
Expect continuity / zero resistance.
| Isolate Mains Power to appliance as per TOPs P4 |
Disconnect the connector to the overheat stat and gas valve
Measure the resistance between the two red wires.
Expect continuity / zero resistance.
Isolate as per TOPs P4
and refit as necessary