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)
Set selector switch to the OFF position
Set selector switch to the 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 39 Vdc (may be a positive or negative voltage).
Test 2. Set selector switch from the OFF position to the DHW/CH position.
Allow boiler to commence its ignition sequence (fan running).
Measure for DC voltage at the same location as test 1.
Expected voltage 0 Vdc.
Expected voltage 39 Vdc (may be a positive or negative voltage).
Test 2. Set selector switch from the OFF position to the DHW/CH position.
Allow boiler to commence its ignition sequence (fan running).
Measure for DC voltage at the same location as test 1.
Expected voltage 0 Vdc.
Isolate as per TOPs P4
and refit as necessary