Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to AC Volts 
Gain access to PCB (use Insulation Mat as required)
CH demand OFF
CH demand OFF
Gas On
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Test1:
With no demand measure the voltage to earth at pin-1 (Blue wire) of connector X21,
Expect approximately 10V AC.
Test2:
CH demand ON
Allow the boiler to attempt to light.
Measure the voltage at Pin-1 again, as the flame lights does the voltage change to approx. 5V AC?
With no demand measure the voltage to earth at pin-1 (Blue wire) of connector X21,
Expect approximately 10V AC.
Test2:
CH demand ON
Allow the boiler to attempt to light.
Measure the voltage at Pin-1 again, as the flame lights does the voltage change to approx. 5V AC?
Isolate as per TOPs P4
and refit as necessary