Fixit was talking about the heating side only.
Problems with a shared return on a new installation
- Thread starter melross
- Start date
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It can only be the return being shared. It wouldn’t work otherwise.
I really don’t understand what you mean. Am I missing something here?
He said there are 3 zones and a zone for the hotwater. They share a return pipe in order to save space. But when the zones are off on the room stats/ the heating comes on the radiators still get hot.
I feel the problem may lie with the wiring.
A non zoned system would obviously only have one return pipe. There would be no control. The only control would be the boiler stat.
I’ve came across old systems with no zones before as such. The coil usually worked on worked on gravity and all the radiators had TRVs. In the summer the boiler would be left on but all radiators were turned off by rad valves, so they still had hotwater. Every now and again I come across these systems, fully pumped or gravity.
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I suppose you mean the OP melross who said that. I assume a zoned system has an automatic valve to isolate each zone (and other controls, eg roomstat). That's what I meant when I said if all the valves are closed I can't see how this unwanted flow can happen.
The house I described is non-zoned (no auto valves apart from the 3-port valve, Honeywell W-plan). The boiler is in the kitchen, ground floor. The return from the HW cylinder comes down from the ceiling. The common return from the upstairs rads also comes down from the ceiling. The common return from the downstairs rads comes up from the floor. Originally the upstairs rads return and the HW cylinder return were commoned, then the downstairs rads return came in - problem! Modified to common the rads returns, then the HW cylinder return comes in.
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I had a similar issue to this resulting in reverse circulation to radiators when only hot water was on. Turned out to to be the bypass valve (in my case a gate valve) in the wrong position with respect to the heating return creating a path for flow through radiators.
Rads may still get hot when hotwater circuit is calling for heat. With a wiring issue this could cause heating zones not to close. He may not have noticed due to the colder weather and heating being on more frequent but know it’s getting milder the problem becomes more
Melross Have you tried this simple test? It will tell you if the problem is caused by the way the returns or connected or by something else, e.g the wiring.
With four zones (inc HW) there are several permutations of zones on/off which need to be tested.
I assume the system has 4 auto valves, one to each CH zone, one to the HW circuit, the boiler/pump starting when any one or more calls for heat. If a CH valve has failed open, clearly that circuit will get hot whenever any of the other 3 calls.
But (having thought about it again) if any of the CH zones has more than 1 rad, the returns on that zone must still be commoned before the HW return. If, for reasons of layout, the CH returns are brought local to the boiler, or the HW return is close to the rads, that may not be the case, resulting in a problem like I had. If that is the case, it might have happened because it made the plumbing more convenient, and the consequences weren't considered.
To add to the above post - what happens if it's piped wrong is the HW return entering the other pipe has 2 ways to go - the "right" way, to the boiler, or the other way, through one set of rads in the reverse direction, then the other set in the forward direction and back to the boiler. If you do a sketch you can easily see it.
I think that's the most likely explanation for what's going on here. It would help if melross posted a schematic (already requested by FiremanT) but it might not be easy to do, as some of the pipes and connection points could be out of sight/inaccessible.
Thanks so much for all your comments. I don’t think it will be possible for me to draw a schematic as I’m not technical and there are many long pipe runs It’s a large installation. The technician is returning later today and I plan to show him all your comments. The installation hasn’t been commissioned yet and won’t be until it is working as it should be. Thanks again all, very helpful indeed.
OK, keep us posted!
Quick update. Technician been back in touch. One solution he wants to try is fit a less powerful pump as he feels he has over-sized the current pump. Not sure if this is the right solution or not? We have 21 rads and a very long house so I would suspect we need a fair sized pump. We will see!
Highly unlikely IMHO.
If he's from the installers, I would ask (or demand!) his firm produces a schematic. If they can't, because they don't know how they plumbed it, that says something.
If he was a knowledgable "technician", he would have calculated the flow and head of your system and sized the pump correctly.
I agree no way. I’m guessing he said the pumps that powerful it pushes passed the zone valves?
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