ChrisR said:
Your response to my last advice was that you would try repressurising or change the boiler - what's the point of asking for advice if you're going to ignore it?
In fairness - I don't think I can do everything everybody has suggested - for a start I am sure that some of the advice will conflict with other advice and in any case practicalities have to be taken into account - including the fact I am incapable/unwilling to "DIY" when it comes to CH plumbing and am trying to reduce the impact on the rest of the house
In fact I have probably paid more heed to your comments than some of the others.
I am at the moment trying to get the engineer to give more consideration to the possibilty of the problem being on the inlet side - which fits in with your comment about "Can you get to the pipes on the inlet side of the pump? If so change a few feet, and the pump valve." One thing I will at least ask him to do is to cut through the inlet pipe where it is magnetic to check for restrictions as whether found or not I think he could repair it fairly easily.
It is difficult as his gut feeling is that it is on the return rather than the inlet - mainly I think because the inlet is very hot and the return cold. My own view is that this may be insignificant if a restriction in the inlet is reducing the flow significantly as presumably wherever it being blocked, the overall flow is the same at all points in the circuit and it may be that so little is getting through at a blockage before the pump that by the time it has got to the return all the heat in the water which does pass has been dissipated.
You have suggested also why the pressurising worked - which is one of the reasons I am considering trying it again - then if all else failed I could change to a pressurised system.
All advice is welcomed, considered as best I can, and passed on where possible.
I guess my main hesitation about some suggestions is that I know it all worked well for years and that the problem should be a development in the system rather than an inherently incorrect plumbing design - even if it ain't great.
And I am sure you would all come up with a different design if starting from scratch to install it.
I have to be fairly subtle in "advising" him - can you imagine how you would feel if a customer was telling you what you should do when you had 30 years of experience - and he was a "suit"