My Ferroli Domina combi is 3 years old and has worked well except that the
ignition gap has to be adjusted every Autumn.

This year the system is generating hot water and hot radiators. But
something is wrong because in CH mode the boiler often fires up, runs for
between a minute and 10 minutes, shuts down, waits for around 30 secs, fires
up, ... The pump keeps running even when the burner shuts down. And in hot
water mode the burner seems to shut down at random unless I keep the tap
very open.

My thoughts were no use:

1. Maybe the ignition gap has closed. No real reason for this because the
symptoms are that the boiler totally refuses to fire up, but it has happened
every year.

2. Maybe a bird's nest in the flue ;-) I've seen boilers fire up and down if
the flue isn't installed correctly and the waste gases get back into the
inlet.

Any ideas where I should look next?

Thanks
Tim