Set Appliance State:
Mains Power Off
Gas Off
Set Multimeter to AC Volts 
CH Demand
Boiler On/Off Switch On
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Allow fan to run and ignition sequence to commence.
Measure the voltage at connector CN1 second from bottom (brown wire) on control PCB to a suitable neutral.
Approximately 8 seconds after the fan starts mains voltage should be present for 3 to 5 seconds. This should repeat 5 times before boiler locks out, with approximately 5 seconds between attempts.
Note:
To reset the boiler switch the boiler On/Off switch Off then back On.
Measure the voltage at connector CN1 second from bottom (brown wire) on control PCB to a suitable neutral.
Approximately 8 seconds after the fan starts mains voltage should be present for 3 to 5 seconds. This should repeat 5 times before boiler locks out, with approximately 5 seconds between attempts.
Note:
To reset the boiler switch the boiler On/Off switch Off then back On.
Isolate as per TOPs P4
and refit as necessary