Are all your flue ways clear on boiler.
It will be the coil.
A shunt pump.
What does your oil pressure and vaccumn gauges tell you is happening.???
Try closing the flue damper a bit more , also ash pit door air screw.
Are the doors sealing correctly?
FFS its only an air vent.
Bung in vent and f/e and new 1/8 or 1/4 vent.
It looks very similar to the cheap and nasty auto vents.
Are we supposed to guess the Boiler/ burner and fire valve details??
I tried but my crystal ball is foggy today!!
What size pipework is feeding these new rads.
It is probably the capacitor needs replacing if it works with a helping hand.
Plenty of videos of this on net.
Run a litre of oil into a clear bottle and check for water in fuel.
Clear hose ???
Which bit are you looking at.
That is defo a long life hose!
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