Glow worm swift flow 75

Can anyone help. i've got a boiler prob. Glow worm swift flow 75
The main burner seems to be blowing out the pilot.
Unlike others i'm not trying to use the central heating ,just hot wwater.
Problem started couple of days ago.
i checked what i could and found a loose bleed nipple on the cold in.

What happens now Switch power to the boiler on pump runs and pressure goes up to 0.6 (with ch and hw off, and c switch off), but goes off after ten secondsish, and pressure drops to 0.2. Get the pilot lit. It's stable. go down to the Grasslin controller put hw on to constant, pilot light stays lit.
Then turn a hot tap in the bathroom on a bit and the boiler sounds like it's firing up but then there's no pilot.Wait a bit and no hot water no matter how long i wait

Any ideas please?
thanks in advance

The fans sometime sieze causing the overheat thermostat to knock the pilot light out.

thanks for the reply i'm guessing thats the fan by the entrance to the flue. i'll have a look in the mrning and post back progress
thanks

Use the filling loop to get the pressure up to about 1 bar, too. See faq section.

Thanks soo much ollski, spot on.
kind of makes sense now ...thanks again

great site ...