Combi boiler doesn't realise it's already lit
I believe it is fairly normal for the igniter to continue to fire for several seconds after ignition, I guess this is because it takes a while for the flame sensor to heat up - and probably also for performance/safety reasons.

Boilers have a flame-sensor, it sounds like your has failed. You can buy replacements.

I think this is a job most people leave to a boiler service technician, you need special tools (e.g. multimeter with microamp range) to check those sensors.

Gas appliance repair is safety critical, probably best left to those with training and experience.


19 = "detection electrode"
20 = ignition electrodes.
See manual


A07 = flame detector.
A09 = flame detection circuit.
A10 = flame indicator LED - I'd check this is "on" after 5 seconds of successful ignition.

Don't rule out other causes, boilers shut themselves down for lots of reasons, maybe the flue is iced up or the water pump isn't operating.

The manual contains a troubleshooting flowchart and a parts list that includes the flame sensor.