Alpha 30CDS. Circulation issues. pressure gauge flickering. loud banging

[armyash]

Ok went to this boiler on Friday, loud banging and going to lock out.

Flow getting hot, nothing coming back.

Went back today, fitted new expansion vessel - external of boiler as not enough clearance to get old one out.

It hasn't helped, the boiler will run for longer before going to lock out but still banging quite badly.

Also tried a new pump but made no difference.

I was there for 4 hours today and I'm stressed out. Any pointers?

A bit of info. For a short period, with just hw on it was circulating properly and coming back to the boiler.

Went to CH only and back to not circulating, some rads were getting hot but just not going all the way back.

Also there is a radiator on the landing (on the outer wall of the airing cupboard) the return pipe off this rad tees off the coil on the cylinder. It looks like this goes back round and links up with the flow, not sure i have explained that very well but the customer kept saying that it was a heat link?? I have tee'd the new ex vessel in on the return pipe from this rad as it is the only return pipe accessible without lifting floorboards.

Any help appreciated. Thanks

 

[Simon F]

the flickering pressure valve means it is flashing to steam,
so no circulation water boiling inside boiler to steam.
motorized valve issue?
seriously sluged up radiators?

 

[armyash]

the flickering pressure valve means it is flashing to steam,
so no circulation water boiling inside boiler to steam.
motorized valve issue?
seriously sluged up radiators?

Went back today, motorised valve is a possibility. Had a couple of other lads there who have more boiler experience than me. Reckon heat exchanger has had it, they have quoted for a new boiler. Might be getting done Friday.