Set Appliance State:
Mains Power Off
Set Multimeter to DC Volts 
Turn Hot Water Tap On
Boiler On/Off Switch ON
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
With the DHW Tap fully open and the DHW Temperature Potentiometer set to maximum, measure the DC Voltage across the Red wire and Black wire on the Stage 2 Gas Valve Solenoid (solenoid 3).
The voltage obtained should be approximately 24 V DC.
The voltage obtained should be approximately 24 V DC.
Isolate as per TOPs P4
and refit as necessary