Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to DC Volts 
Turn Hot Water Tap On
Gain access to PCB (use Insulation Mat as required)
Selector switch set to OFF position
Selector switch set to OFF position
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Test 1.
Measure for DC voltage across the two reds leads of connector X16.
Expected voltage approximately 37V DC (may be a positive or negative voltage).
Test 2.
Turn selector switch to DHW & CH position.
Allow boiler to commence its ignition sequence (fan running).
Measure for DC voltage at the same location as test 1.
Voltage should be now be approximately 0V DC.
Note.
1. Ensure a good connection is made as misdiagnosis will occur.
2. Appliance may enter lockout during this test, reset as required until test is complete.
Measure for DC voltage across the two reds leads of connector X16.
Expected voltage approximately 37V DC (may be a positive or negative voltage).
Test 2.
Turn selector switch to DHW & CH position.
Allow boiler to commence its ignition sequence (fan running).
Measure for DC voltage at the same location as test 1.
Voltage should be now be approximately 0V DC.
Note.
1. Ensure a good connection is made as misdiagnosis will occur.
2. Appliance may enter lockout during this test, reset as required until test is complete.
Isolate as per TOPs P4
and refit as necessary