Reverse circulation new build

[fixitflav]

t was, you linked it in your post (although part of the url at the start was ******* for some reason)

Interesting, you live and learn!

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.

Having 2 zone valves doesn't necessarily prevent the problem. I'll do another sketch tomorrow.

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)

But following the forum's recommendations, it cured the problem.

 

[johnduffell]

Having 2 zone valves doesn't necessarily prevent the problem. I'll do another sketch tomorrow.

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.

But following the forum's recommendations, it cured the problem.

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.

 

[johnduffell]

Then either drop to the rads downstairs or up out of the floor to the rads upstairs.

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?

 

[Jeff]

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.

 

[johnduffell]

so the piping looks ok in the garage then and follows the 3 t rule?

No, that's what we are trying to establish

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

Correct, and correct.

 

[Jeff]

Hi,
Thanks for the help with this. I've got a response from the plumber. The rad returns all go into the one return (interleaved)

 

[Jeff]

Hi

He’s saying to put one way valves on all the radiators now. Is this the best approach?

 

[johnduffell]

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.

 

[ShaunCorbs]

No that's a bodge

 

[Jeff]

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?

 

[fixitflav]

No, that's what we are trying to establish

Correct, and correct.

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.

The thread identified in your #12, can you locate it? I found it the other day by searching for melross (the OP) but it seems to have disappeared. I think it would interest Jeff. One poster (and possibly the installer) suggested a non-return valve, somebody else said (a la ShaunCorbs above) why install extra kit, which could cause problems later, when it wouldn't be needed if the job were done right. The installer made some futile suggestions like smaller pump, but finally modded the pipework. Unfortunately we never saw a pipe layout schematic.
Per my #21, I won't bother posting another sketch as you clearly understand what I mean.
On this job. I haven't got my head round all the piping, but with the cylinder next to the boiler you'd have to make a serious effort to pipe it wrong! On the other job I suspect it was a case of a convenient connection point.
On latest photo, I can see the right-hand pipe into the boiler is an elbow, not a tee, so that theory doesn't hold.
I think I'd like to see a pipework schematic before taking the plumber's word that it's done correctly! I don't know what interleaved means in this context, but to put it simply, the HW cylinder return should join the pipework last, after all other flows are commoned.
Another thought - is it possibly something simple like one of the zone valves failed open?

 

[Jeff]

Hi,

Interleaved was mention in a question:

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?

The answer from the plumber was B.
He suggested one way values on each radiator, but people have suggested this is a botch job. So I’ve asked him to pipe it as per A above. Hopefully this should resolve the issue. Anyone think different before they start tomorrow? Sounds silly having to ask when I have the plumber, but I’ve been messed about so much. Appreciate everyone’s input!

 

[johnduffell]

the HW cylinder return should join the pipework last, after all other flows are commoned.

You've helped me understand, now maybe ii ca help you in return!
Don't be confused by the dhw circuit being special, the issue can occur between any two circuits. In this case delete the cylinder completely, and the tees rule applies to the returns from the two circuits. That is, the return needs to have a single tee/joining point for the whole of each circuit.

 

[ShaunCorbs]

Please don't spam the forum with links

 

[fixitflav]

You've helped me understand, now maybe ii ca help you in return!
Don't be confused by the dhw circuit being special, the issue can occur between any two circuits. In this case delete the cylinder completely, and the tees rule applies to the returns from the two circuits. That is, the return needs to have a single tee/joining point for the whole of each circuit.

In the case of a 3-port valve, or a CH zone valve, feeding all CH circuits, the problem doesn't arise, as all circuits are being fed, in the right direction, at once. I hadn't thought about it, but you're right, with a zone valve for each CH zone it can happen if piped in a certain way. Interesting, as one might think individual zone valves would be better. Of course it would be less of a problem than rads getting hot when DHW called, as if heat is wanted in one zone, it's unlikely to be a big issue if another zone gets warm. Not that the mistake shouldn't be avoided. But in hot weather the last thing you want is rads getting hot, apart from the cost of the gas.

 

[fixitflav]

Hi,

Interleaved was mention in a question:

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?

The answer from the plumber was B.
He suggested one way values on each radiator, but people have suggested this is a botch job. So I’ve asked him to pipe it as per A above. Hopefully this should resolve the issue. Anyone think different before they start tomorrow? Sounds silly having to ask when I have the plumber, but I’ve been messed about so much. Appreciate everyone’s input!

Re-reading your original post, the problem is one set of rads getting hot when the other set is calling. A more common problem is rads getting hot when DHW calling. But if it's piped as attached sketch that could give your symptoms. From the photos posted I don't think it's possible to be sure it isn't. The fault could be remote from the boiler room.
A schematic of the complete system would be useful, but might need a bit of investigation.

 

[johnduffell]

Please don't spam the forum with links

sure - I only posted it once but I assume it's been entered into the "swear words" list 😉 now someone has deleted all the links - it's a relevant information regarding this thread so it should be linked somewhere.
I assume the worry is that everyone will like there more than here and stop visiting, but I doubt there's any risk of that from what I've seen.

 

[ShaunCorbs]

sure - I only posted it once but I assume it's been entered into the "swear words" list 😉 now someone has deleted all the links - it's a relevant information regarding this thread so it should be linked somewhere.
I assume the worry is that everyone will like there more than here and stop visiting, but I doubt there's any risk of that from what I've seen.

Yea me, all the links were broken due to the forums policy on advertising other forums

 

[johnduffell]

Yea me, all the links were broken due to the forums policy on advertising other forums

What do they define as advertising? I for one am only interested in helping people and learning.

 

[ShaunCorbs]

What do they define as advertising? I for one am only interested in helping people and learning.

@Lou