Set Appliance State:
Mains Power Off
Set Multimeter to Resistance 
Turn Hot Water Tap On
Gas On
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Allow boiler to heat DHW to at least 50°C.
Turn hot tap OFF.
Remove one the yellow wires attached to the DHW thermistor sensor.
Measure the resistance across the terminals of the sensor.
Is the resistance measured below 4.5 kOhms?
Turn hot tap OFF.
| Isolate Mains Power to appliance as per TOP's P4 |
Remove one the yellow wires attached to the DHW thermistor sensor.
Measure the resistance across the terminals of the sensor.
Is the resistance measured below 4.5 kOhms?
Isolate as per TOPs P4
and refit as necessary