Reverse circulation new build

[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