I have a gravity-fed CH and hot water system on a Y-plan.
The boiler is working fine and the hot water is heating without a problem however I can't get water around the CH circuit at all.
When we moved into this house neither the hot water nor the central heating were working. The hot water is working after replacing the mid-position actuator for the 3-port valve.
See the diagram at the bottom.
If I run water round the hot water circuit (coloured red) until it gets hot, then switch on the central heating, then I can feel hot water flush into the first six inches to a foot of pipe then it stops and sits there slowly cooling.
It seems like there is an air lock somewhere but I just don't know where.
I have flushed mains pressure water around the system, into and out of radiators on all floors. Usually while doing this I have pushed into the flow and out of the return or vice versa with all radiators shut down so the water must flow around the main circuit. I have also at times blocked off the expansion and refill pipes to the header tank while flushing the system. I have done this more times and in more ways than I can remember.
When testing the system after flushing it I have refilled the radiators, opened all the radiator valves, put on the hot water to get hot water circulating then switched the valve over to the CH circuit (by switching to "hot water and central heating" and turning down the thermostat on the hot water). I always get the same result (a little water flushing into the pipe, then stopping).
When I refill a radiator that I have drained. I often find the system has negative pressure and starts sucking. Usually I have to pump water into the central heating though a drain valve or radiator valve in order to refill and bleed all the radiators.
I have drained the system down and haven't found any sludge when doing so or when draining the radiators (the water is a little black in the bottom of the radiators that is all).
Referring to the diagram I have included:
* the red pipes are part of the hot-water heating loop and are circulating fine
* I have drained water out though the purple pipe and pulled hot water though, so these appear to be fine.
* Whatever blockage is causing the problem must be on a part of the circuit that is common to all of the radiators since no water is circulating around the CH system at all.
* This only leaves the pipes I have coloured blue. In the diagram this looks like quite a lot of pipe but it is actually about eighteen inches to two feet of pipe which is dead level.
I have had two plumbers in. The first one suggested replacing all of the pipes for the ground floor radiators. It seems obvious that that can't be the problem. I think the only reason he picked this is that he can get to these pipes. Perhaps I'm being unfair.
The second plumber has so far basically just repeated what I have done and and said "this is very strange".
I have also talked to a few friends who have plumbed their own homes, all so far a pretty baffled.
I think that my next step might be to start cutting pipes and short-circuit the CH system to see whether I can get water pumping round it but I a loathe to do that. I had never touched CH system before this.
All input and suggestions gratefully receeived.
The above diagram is simplified and misses some details, ask me is anything is unclear.
I'm not sure exactly where the expansion over-flow connects into the system. That's something I will check.
PS. I'm pretty tired right now. I hope this post makes sense. I will re-read it tomorrow.
The boiler is working fine and the hot water is heating without a problem however I can't get water around the CH circuit at all.
When we moved into this house neither the hot water nor the central heating were working. The hot water is working after replacing the mid-position actuator for the 3-port valve.
See the diagram at the bottom.
If I run water round the hot water circuit (coloured red) until it gets hot, then switch on the central heating, then I can feel hot water flush into the first six inches to a foot of pipe then it stops and sits there slowly cooling.
It seems like there is an air lock somewhere but I just don't know where.
I have flushed mains pressure water around the system, into and out of radiators on all floors. Usually while doing this I have pushed into the flow and out of the return or vice versa with all radiators shut down so the water must flow around the main circuit. I have also at times blocked off the expansion and refill pipes to the header tank while flushing the system. I have done this more times and in more ways than I can remember.
When testing the system after flushing it I have refilled the radiators, opened all the radiator valves, put on the hot water to get hot water circulating then switched the valve over to the CH circuit (by switching to "hot water and central heating" and turning down the thermostat on the hot water). I always get the same result (a little water flushing into the pipe, then stopping).
When I refill a radiator that I have drained. I often find the system has negative pressure and starts sucking. Usually I have to pump water into the central heating though a drain valve or radiator valve in order to refill and bleed all the radiators.
I have drained the system down and haven't found any sludge when doing so or when draining the radiators (the water is a little black in the bottom of the radiators that is all).
Referring to the diagram I have included:
* the red pipes are part of the hot-water heating loop and are circulating fine
* I have drained water out though the purple pipe and pulled hot water though, so these appear to be fine.
* Whatever blockage is causing the problem must be on a part of the circuit that is common to all of the radiators since no water is circulating around the CH system at all.
* This only leaves the pipes I have coloured blue. In the diagram this looks like quite a lot of pipe but it is actually about eighteen inches to two feet of pipe which is dead level.
I have had two plumbers in. The first one suggested replacing all of the pipes for the ground floor radiators. It seems obvious that that can't be the problem. I think the only reason he picked this is that he can get to these pipes. Perhaps I'm being unfair.
The second plumber has so far basically just repeated what I have done and and said "this is very strange".
I have also talked to a few friends who have plumbed their own homes, all so far a pretty baffled.
I think that my next step might be to start cutting pipes and short-circuit the CH system to see whether I can get water pumping round it but I a loathe to do that. I had never touched CH system before this.
All input and suggestions gratefully receeived.
The above diagram is simplified and misses some details, ask me is anything is unclear.
I'm not sure exactly where the expansion over-flow connects into the system. That's something I will check.
PS. I'm pretty tired right now. I hope this post makes sense. I will re-read it tomorrow.
