Set Appliance State:
Mains Power Off
Set Multimeter to AC Volts 
Turn Hot Water Tap On
Boiler On/Off switch Off
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Boiler On/Off switch On.
Reset lockout if necessary.
Allow fan to run and ignition sequence to commence.
Measure the AC voltage between the flame sense electrode lead at the flame sense electrode and a suitable earth point.
Observe multi-meter, voltage should read
approximately 55 volts AC.
As burner ignites voltage should reduce to
approximately 35 volts AC.
Reset lockout if necessary.
Allow fan to run and ignition sequence to commence.
Measure the AC voltage between the flame sense electrode lead at the flame sense electrode and a suitable earth point.
Observe multi-meter, voltage should read
approximately 55 volts AC.
As burner ignites voltage should reduce to
approximately 35 volts AC.
Isolate as per TOPs P4
and refit as necessary