Before I start, I have a fairly intimate knowlege of my system, having done a large amount of work on it myself. I think I understand what the problem is, but I don't know how to resolve it. So here goes:
Boiler in cellar. Output spilts just after the boiler by means of Horstmann flowshare valve. Heating side splits and goes in separate directions. Water side heads off upstairs alongside one part of the heating circuit. The returns for these last 2 come back downstairs side by side join the return from the other part of the heating circuit before finally before going back into the boiler.
During the summer I have noticed the radiators getting hot while the water programmer is demanding heat from the boiler. This at times drives me mad. I am having a purge on wasting energy at the mo and sorting this is high on the list.
I had to replace the programmer and flowshare a while back and thought this may also solve the problem if the old valve perhaps wasn't closing 100%, but still got exactly the same symptoms with the new valve. So I'm sure its not the valve and the program controller connections.
What I have since discovered is that the return pipe from the upstairs heating is at roughly the same temperature (to touch) as the return from the water, while the heating flow to upstairs is notably cooler. This suggests that some of the water retunring from the cylinder tank flows back up the heating return, rather than all of it going into the boiler. What I can't fathom is where this is flowing to as the other end of the circuit should be blocked by the flowshare valve, so this shouldn't happen. It just doesn't make sense.
Has anyone else come across this. Can you fit some sort of 22mm one way valve to stop return going the wrong way up an ajoining return pipe on a different circuit, rather than back into the boiler?
Cheers