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Discussion in 'Central Heating Forum' started by Jeff, Jun 5, 2018.
Discuss Reverse circulation new build in the Central Heating Forum area at UKPlumbersForums.co.uk.
Separate issue, expansion relief pipework teed in after the tundish
Glad you found that, I thought it was on a different forum I visit! Or I would have just referred OP to it, where it was discussed at some length. And the problem was as I and others predicted.
I don't believe Jeff's system is piped differently, at least not different enough to avoid the problem. See my reply to his #14.
I've attached hand sketch to illustrate what I was saying.
it was, you linked it in your post (although part of the url at the start was ******* for some reason)
Yes I realise what condition you mean now that you mention, basically with two heating loops joined after the diverter valve, and teeing into different point of the DHW return.
in this case we can see two zone valves in the photo, so that doesn't apply.
Regarding the OP on the other forum, he stated there are 3 zones and HW, of course that doesn't rule out the configuration you mention in all of the zones separately, but unlikely (he stated if any of the zones are on, it migrates to both the rest of them)
I can't quite see the Tee mentioned by fixitflav so I'm going to offer an alternative viewpoint for consideration if that's alright with everyone - I think the "return" from above is shared between the two zones, and when downstairs is on, water from there rises upstairs due to convection. It appears that there's a check valve on the visible section of return, presumably to keep the bypass from causing convection, but not protecting the two CH circuits from each other.
Any chance of a photo of where the downstairs return joins the rest of the return?
Sorry the photo isn;t the best. I had trouble trying to get it all in. The boiler is in the garage on ground floor all pipes are run into the first floor floor. Then either drop to the rads downstairs or up out of the floor to the rads upstairs. The return looks like the only return.
I've added a mother photo of all pipes going up into the ceiling(first floor floor) the lagged pipe right under the boiler is the only one there is no other joining it to the right (i've added another photo)
Interesting, you live and learn!
Having 2 zone valves doesn't necessarily prevent the problem. I'll do another sketch tomorrow.
But following the forum's recommendations, it cured the problem.
Interesting, so the configuration you mention may exist within a zone. I thought unlikely but now I can see it would be easy done.
So in this OP's case we are looking for the downstairs circuit goes all the way back to the return, and on the return leg, there are two distinct points where upstairs rads tee in. Therefore due to the moving water there's a small pressure difference across the two upstairs returns causing a small flow.
True, but the OP there repiped all the returns separately unnecessarily in that case.
If the forum's recommendations were true, he could have still had a shared return as per original, but just made sure that all pipes on each circuit joined together first, then joined the main shared return.
Interested to see what the result is on this one though.
As per fixit and my exchange, a question arises -
That return pipe, do the upstairs and downstairs rads:
A) all combine into two separate pipes, before joining together in a single place and flowing into the return pipe visible, or
B) are they interleaved so some (but not all) upstairs pipes are combined with some (or all) the downstairs pipes, and the remaining upstairs pipes combine later in the run?
Hi so the piping looks ok in the garage then and follows the 3 t rule? And you think it’s the way the pipes have been run. So if they have the rads from both upstairs and downstairs connecting onto to the same return it’s a problem(interleaved) ? Should they be 2 separate returns for each zone that then combine to the one return that goes back to the boiler? I’m not sure which way it’s been done, but can ask the plumber.
No, that's what we are trying to establish
Correct, and correct.
Thanks for the help with this. I've got a response from the plumber. The rad returns all go into the one return (interleaved)
He’s saying to put one way valves on all the radiators now. Is this the best approach?
Sounds like the problem is exactly what fixitflav said in the first place
I would say best depends on your point of view. That is probably the cheapest option at this stage. But extra valves would reduce the reliability of the system slightly.
No that's a bodge
What affect will it have? I know it will stop rads warming, is it just that the boiler pump will ware out quicker?. I’m not sure how difficult it would be to run another return would it mean taking all the ceilings down?
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