Set Appliance State:
Set Multimeter to DC Volts 
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Mode Selector Switch to DHW position
Disconnect Sense Electrode Lead from Ignition Control Box
Mode Selector Switch to DHW position
Disconnect Sense Electrode Lead from Ignition Control Box
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Measure DC Voltage between end of Sense Electrode Lead and disconnected terminal of Ignition Control Box.
The voltage will be approximately 0V before burner ignition and should be greater than 10V DC after ignition.
MAINS POWER OFF.
Reconnect Sense Electrode Lead after test.
The voltage will be approximately 0V before burner ignition and should be greater than 10V DC after ignition.
MAINS POWER OFF.
Reconnect Sense Electrode Lead after test.
Isolate as per TOPs P4
and refit as necessary