Set Appliance State:
Gas Off
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Boiler ON/OFF Switch OFF
Ensure DHW is cool
Disconnect yellow wire from DHW sensor
Ensure DHW is cool
Disconnect yellow wire from DHW sensor
Measurement:
Measure resistance across the terminals of the DHW Sensor.
Resistance should be between 3-30 kOhms.
Resistance should be between 3-30 kOhms.
Isolate as per TOPs P4
and refit as necessary