Reverse circulation new build

[Jeff]

Hi,
I'm looking for a little help. I bought a new build and have heating issues since we moved in. The builder wants the installer to resolve the issues, but hes been back now about 5 times and still the issue persists. I was hoping for a little advice. We have 2 circuits 1 upstairs and 1 downstairs. When the downstairs is on the rads upstairs start getting hot one by one via the return. Whats the best way to get to identify whats causing the issue. Is this issue generally caused by the way the pipes have been run i.e. 22mm to microbore or is it generally the pipework around the boiler. I'm reluctant to pay someone to resolve it, as its the builders responsibility but the plumber the builder keeps sending (the installer) is not fixings the problem and seems to not be able to identify the issue either. Any help or direction would be greatly appreciated.

 

[ShaunCorbs]

It's the plumbers fault for teeing in the returns wrong

What system do you have combi or unvented eg cylinder ?

 

[Stigster]

Plumber needs to abide by the "Three Tee Rule". This thread covers it fairly well I believe.

3 tee rule anyone?

 

[Jeff]

It’s an unvented cylinder and Worcester condenser boiler. I could post a photo of the pipe work near the boiler tonight if that would help identify. I’ll be honest there are. Lot of pipes coming and going

 

[Stigster]

Photos would be helpful almost certainly. If I can't work out the problem somebody here will. They are a good lot.

 

[johnduffell]

If the installer understands gravity they should be able to work it out. If there's hot water below cold in a vertical pipe, they will start to mix even if no circulation.
Agree that photos would help, ideally annotated with which pipe is which if not clear.

 

[Jeff]

Thanks everyone. I’ll take a photo and post tonight. Your help is much appreciated!!

 

[fixitflav]

If the installer understands gravity they should be able to work it out. If there's hot water below cold in a vertical pipe, they will start to mix even if no circulation.
Agree that photos would help, ideally annotated with which pipe is which if not clear.

But it's not gravity or convection that causes this problem. All the CH return pipes must be commoned before the HW cylinder return comes in. My first house in 1973 had it, the builders/plumbers had piped it wrong. Got them to change it and everything OK.

 

[johnduffell]

But it's not gravity or convection that causes this problem.

Oh right maybe i misunderstood it then! So what does cause it?

 

[fixitflav]

Oh right maybe i misunderstood it then! So what does cause it?

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. A schematic, or a photo if the pipes are identified would be useful.

 

[ShaunCorbs]

Is it a 2 port or 3 port system?

 

[johnduffell]

through one set of rads in the reverse direction, then the other set in the forward direction and back to the boiler.

interesting, so upstairs has a closed zone valve, but somehow the backflow through the upstairs circuit can get through to the boiler by going forwards through the downstairs circuit (a second time?)

I'm even more confused, and I'm not quite sure what diagram to draw, but I'd agree the piping would be seriously messed up to have that kind of flow.

 

[johnduffell]

having read your original post, your 1973 system was different and had two heating loops on one zone but teed in separately. In this case the OP has two heating circuits on two zones, so that circulation wouldn't happen.

From reading your description, your system could indeed have also suffered from convection on top of the circulation you mentioned, as the hot return from the DHW side connected with a vertical pipe going back to the upstairs rads:

"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​

"

 

[Jeff]

Hi All,

Here is a photo of the pipework. I've labelled everything that is labelled on the pipes. Any ideas if there is an issue here?

 

[fixitflav]

Hi All,

Here is a photo of the pipework. I've labelled everything that is labelled on the pipes. Any ideas if there is an issue here?

View attachment 33772

I think the pipe labelled Return is upstairs return. I can see where the HW cylinder return comes in, below the boiler. No pipe is labelled Downstairs return, but my guess is it is off the photo to the right. I can just about see a tee right on the edge of the photo. If that's it, that's the source of the problem, IMO.

 

[Christopher buzzard]

Separate issue, expansion relief pipework teed in after the tundish

 

[fixitflav]

having read your original post, your 1973 system was different and had two heating loops on one zone but teed in separately. In this case the OP has two heating circuits on two zones, so that circulation wouldn't happen.

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.

 

[johnduffell]

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.

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

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.

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)

 

[johnduffell]

Any ideas if there is an issue here?

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?

 

[Jeff]

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)

 

[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.