Boiler flame jumping/thumping.

This is not right. If you could describe the 'outdoor vent' that would help. Make and model would be a bit helpful too.

For one moment I thought you were peering out through the kitchen window and saw flames!

Possible. Worth checking the vent is fitted correctly before going any further. Also check the fga A ports in the flue are sealed.

There's also something in the back of my mind saying "gas regulation". Perhaps the gas control module/valve is faulty or has dirty contacts and causing a fluctuating flow of gas to the burner?

I doubt it's due to dirty jets as the boiler was serviced only a year ago.

sponix

It was an Ideal make, wall mounted non-condensing boiler. Air in + vent is via concentric vent, via kitchen wall to triangular/circular metal external vent. I looked but didn't touch as alcohol and DIY and even alcohol and gas repairs do not go well.

The thumping is not loud, my mate had never noticed it, just thought it was normal boiler noise.

Actually as I typed, he phoned, had it sorted, it was a crack/tear in a flue pressure sensor pipe and or sensor causing gas valve to chatter on and off. His "man" sorted it and iit no monger thumps,

Oh good, must be terrible having a thumping monger.

Owain

My m8 got thumped by a monger once.

sponix