I have a two storey house with 14 radiators. 6 upstairs and 8 downstairs. The pump is a Grundfoss 15-60 and is new. The system is piped with 10mm microbore, mostly plastic but a couple of radiators have copper pipe. I have had problems with pipes clogging with black muck and have just flushed it out after using sludge remover.
My problem is that the upstairs radiators are now working ok, the hottest closer to the manifold but all reasonably hot, whilst the downstairs radiators are either cool or cold (mostly the latter).
Before flushing the system most of the downstairs radiators worked ok, the ones furthest from the manifold being the blocked, cool ones (Cool radiators have been washed out with a hosepipe).
The water pressure in the return pipes seems greater than the pumped hot side pipes. I suspect that the system needs balancing but I don't know how to do it. Can anyone help please?