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Situation is that my Central Heating (30 years old) is not functioning properly. Given my best shot at describing it - but I know nothing about plumbing 
This is an open vented system with an F&E tank and a conventional S plan layout exactly as per this drawing according to the plumber:
http://www.gasman.fsbusiness.co.uk/images/sppic.jpg
The system uses 28 mm going down to 15 mm with 10 mm pipes off this to radiators
Boiler (ten years old) is in garage, pump and F&E in cylinder cupboard.
Symptoms are that only 3 radiators are now getting hot. (two in upstairs bathrooms, one on landing). Main bedroom radiator is tepid. The feed pipe to the tepid radiator is hot but the return cool. Where radiators are completely cold both pipes are also cold.
Initially the main problem when the syatem started to misbehave was that the main radiator (huge) in the lounge was cold at the bottom but hot at the top. I had had this problem before, about a year ago, with other radiators also not warm enough and a pressure flush (different plumber
) got it working fairly well again (although certainly not perfectly).
Water is only hand hot from cylinder (stat set to 160 degrees)
Plumber has tried checking pump and motorised valves and flushed every radiator individually (but not pressure flushed entire system which he is not greatly in favour of). He has also tried running it as heating only (by turning down the cylinder stat as the simple programmer does not allow this) and with several rads shut off.
He feels that the problem must be a blockage in the return as the feed is hot but the return only warm but does not know if this is air or sludge.
Only positive actions taken has been to replace a vent into the F&E tank which was removed (I think) several years ago when it was pumping over and the F&E tank was full of extremely hot water casuing a major condensation problem. The tank now gets pleasantly warm when the system has been on for some time but shows no sign of overheating. I do not think it is now pumping over
He has also filled a vent to the a long horizontal run of the return pipe near the boiler to try and get rid of air from the system. Over the course of two days the system has been drained and refilled several times - with difficulty. I think he has had to resort to using water from the mains to do this rather than simply from the normal cold feed.
Picture of cylinder cupboard showing new vent into F&E tank
www.paulhodson.f2s.com/cupboard.jpg
Close up of pump and valves (somewhat obscured by shower pump)
www.paulhodson.f2s.com/pumppic.jpg
However, as the system has worked correctly in past I asume all plumbing is basically correct
Both days of his visit, by the end of the day the downstairs radiators had started getting somewhere from fairly warm to tepid depending on location - but then cool down again even though the heating is still running and are eventually literally icy cold without any sign of heat in them.
The next morning they stay permanently icy with just the same three heating up as before. This would seem to me to suggest that it might be air getting into the system again but I don't know how or where. otherwise presumablly sludge is resettling.
The situation is worse than when he started - although I have every confidence in him - local well respected guy who is both embarassed and tearing his hair out!
I suppose my main confusion is that three radiators appear to work more or less normally but no others. If the blockage is in the return I would have expected all to have the same problem and if in the 10 mm radiator feed pipes it seems odd they should all block up at the same time.
It is also odd that it seemed to work slightly better before the vent into the F&E was refitted - but this obviously should be there.
Money is not an issue - I would try everything up to replumbing the entire damn system - but I cannot even imagine the difficulty and mess to the house in this process so am looking for any bright ideas he can try!
Sorry for the long post - tried to explain everything - but no doubt failed!
This is an open vented system with an F&E tank and a conventional S plan layout exactly as per this drawing according to the plumber:
http://www.gasman.fsbusiness.co.uk/images/sppic.jpg
The system uses 28 mm going down to 15 mm with 10 mm pipes off this to radiators
Boiler (ten years old) is in garage, pump and F&E in cylinder cupboard.
Symptoms are that only 3 radiators are now getting hot. (two in upstairs bathrooms, one on landing). Main bedroom radiator is tepid. The feed pipe to the tepid radiator is hot but the return cool. Where radiators are completely cold both pipes are also cold.
Initially the main problem when the syatem started to misbehave was that the main radiator (huge) in the lounge was cold at the bottom but hot at the top. I had had this problem before, about a year ago, with other radiators also not warm enough and a pressure flush (different plumber
) got it working fairly well again (although certainly not perfectly).Water is only hand hot from cylinder (stat set to 160 degrees)
Plumber has tried checking pump and motorised valves and flushed every radiator individually (but not pressure flushed entire system which he is not greatly in favour of). He has also tried running it as heating only (by turning down the cylinder stat as the simple programmer does not allow this) and with several rads shut off.
He feels that the problem must be a blockage in the return as the feed is hot but the return only warm but does not know if this is air or sludge.
Only positive actions taken has been to replace a vent into the F&E tank which was removed (I think) several years ago when it was pumping over and the F&E tank was full of extremely hot water casuing a major condensation problem. The tank now gets pleasantly warm when the system has been on for some time but shows no sign of overheating. I do not think it is now pumping over
He has also filled a vent to the a long horizontal run of the return pipe near the boiler to try and get rid of air from the system. Over the course of two days the system has been drained and refilled several times - with difficulty. I think he has had to resort to using water from the mains to do this rather than simply from the normal cold feed.
Picture of cylinder cupboard showing new vent into F&E tank
www.paulhodson.f2s.com/cupboard.jpg
Close up of pump and valves (somewhat obscured by shower pump)
www.paulhodson.f2s.com/pumppic.jpg
However, as the system has worked correctly in past I asume all plumbing is basically correct
Both days of his visit, by the end of the day the downstairs radiators had started getting somewhere from fairly warm to tepid depending on location - but then cool down again even though the heating is still running and are eventually literally icy cold without any sign of heat in them.
The next morning they stay permanently icy with just the same three heating up as before. This would seem to me to suggest that it might be air getting into the system again but I don't know how or where. otherwise presumablly sludge is resettling.
The situation is worse than when he started - although I have every confidence in him - local well respected guy who is both embarassed and tearing his hair out!
I suppose my main confusion is that three radiators appear to work more or less normally but no others. If the blockage is in the return I would have expected all to have the same problem and if in the 10 mm radiator feed pipes it seems odd they should all block up at the same time.
It is also odd that it seemed to work slightly better before the vent into the F&E was refitted - but this obviously should be there.
Money is not an issue - I would try everything up to replumbing the entire damn system - but I cannot even imagine the difficulty and mess to the house in this process so am looking for any bright ideas he can try!
Sorry for the long post - tried to explain everything - but no doubt failed!
but i`ve done 99% of my jobs right over the last 30 years and the 1% for example where I had badly positioned the feed tank ..........I fixed FOC 
