DIY Doctor UK DIY Forums

I have recently replaced the hot water diaphragm on my Ideal Combi as it was perforated. Hot water and heating were fine for a week or two.

Now the boiler starts knocking when the heating has been running for a couple of minutes. It seems like air as the pressure guage flicks as the noise occurs which seems to be coming from the pump.

I took out the heat exchanger and flushed it but it seemed Ok no sludge.

The rads don't let out much air when bled. Is air the cause and if so, how do I get rid of it?

Thanks.

Auto airvent open ?
vented the pump ?

Did you drain the heating system ? if so did you add inhibitor, 2 or 3 weeks is fairly quick for a kettling problem to occur, but possible - a build up of limescale is causing the noise.