Reverse Circulation when HW On

[fixitflav]

I will re-pipe, can I do this by moving the upstairs return (with valve removed) to the right of tee 2 and tee the return with the towel rad,

You also need to tee the downstairs rads return into the same pipe so that "all the rads returns are commoned before the cylinder return."

do I need to move the cylinder return down. Does either way work?

Not sure what you mean, but the easiest way to achieve it will depend a lot on the house layout.

 

[Daveydub]

If there is a circuit there will be circulation.
If you read again my last post it explains why towel rail reverses when hw on. It also flows through all of the radiators in the right direction. If you turn the towel rail off on your diagram you can then see the alternative route, backwards through upstairs rads and forwards through downstairs. Your check valve prevents this. I think that if you fitted a check valve to the towel rail you would prevent the chattering.

 

[woodpeckerx]

Tee 3 is OK, just needs the cylinder return connection changing to downstream (to the left) of Tee 1.

You also need to tee the downstairs rads return into the same pipe so that "all the rads returns are commoned before the cylinder return."

I'm confused, you said tee 3 is ok yesterday but now saying I need to move that as well so cylinder is downstream of it?

That will be much more difficult as the T is right on top of the boiler return connection.

 

[Daveydub]

Turn the towel rail off and I believe that everything will be fine. Let's start from there.

 

[Daveydub]

confused, you said tee 3 is ok yesterday

Its panto season so
Oh no I didn't

 

[fixitflav]

I'm confused, you said tee 3 is ok yesterday but now saying I need to move that as well so cylinder is downstream of it?

I did, but after a rethink I retracted that in post #10.
For the nth time, make sure all the rads returns are commoned before the cylinder return

As I said, the easiest way to achieve it will depend a lot on the house layout.

 

[fixitflav]

Its panto season so
Oh no I didn't

That was a reply to my post

 

[woodpeckerx]

I did, but after a rethink I retracted that in post #10.
For the nth time, make sure all the rads returns are commoned before the cylinder return

As I said, the easiest way to achieve it will depend a lot on the house layout.

Ahh, ok.

I know the returns should all be commoned before but that is the most difficult to acheive due to the return T on top of the boiler, it was probably wishful thinking I could leave that tee.

 

[woodpeckerx]

If there is a circuit there will be circulation.
If you read again my last post it explains why towel rail reverses when hw on. It also flows through all of the radiators in the right direction. If you turn the towel rail off on your diagram you can then see the alternative route, backwards through upstairs rads and forwards through downstairs. Your check valve prevents this. I think that if you fitted a check valve to the towel rail you would prevent the chattering.

Yes I can see that paths you mention, so it seems the options (other than fixing all the pipework) is turn the towel rad into an always on by connecting it to the boiler feed after the pump or fitting a check valve to prevent the reverse circulation.

I will turn the towel rail off as you suggest and report back.

 

[fixitflav]

the most difficult to acheive due to the return T on top of the boiler,

Can you post a photo? Usually the connections are remote from the boiler, into one common return pipe. If it's any help, a couple of pics of my boiler. The 22mm pipe to the left is the rads return, up and downstairs commoned further back. The cylinder return is the top 28mm pipe. Boiler flow top, return bottom. It's a conversion from a gravity HW system, hence the 28mm pipes.

 

[woodpeckerx]

Can you post a photo? Usually the connections are remote from the boiler, into one common return pipe. If it's any help, a couple of pics of my boiler. The 22mm pipe to the left is the rads return, up and downstairs commoned further back. The cylinder return is the top 28mm pipe. Boiler flow top, return bottom. It's a conversion from a gravity HW system, hence the 28mm pipes.

This is tee 3 at the top of the boiler, 22mm coming through the ceiling is the combined cylinder and upstairs return from tee 1, at this point we are about 4m downstream of the cylinder.

Tee 3 centre joins this with the 22mm return from the downstairs rads and the bottom of the tee goes into the the boiler return via the Spirotrap.

 

[woodpeckerx]

Turn the towel rail off and I believe that everything will be fine. Let's start from there.

Towel rail off and all rads remain cold with HW on.

Edit:

But as CH kicked in, the check valve in the upstairs return started to initially chatter.

 

[Daveydub]

Towel rail off and all rads remain cold with HW on.

With your check valve in place this is as expected.
If you fit a check valve to t.rail circuit all should be well but t.rail will then only come on with heating.
If you can move the t.rail flow to anywhere between the pump and the 2 diverter valves you would have all year round operation and you would not need the check valve.
On the drawing, into the flow to by-pass is perfect but maybe not in real life.

On the drawing it would be easy to connect down rads to boiler flow, incorporate a zone valve and have seperate control of heat down & heat up.
In real life this may not be practical but it would make your tees fine as they are and no check valve required.

What is happening is that, water flows from tee 2 to tee 1. Some water will take the more complicated route from tee 2, backwards through towel rail, forwards through rads up and back to tee 1. We will call that a(lternate) r(oute)1
With t.rail turned off and no check valve water flows from tee 1 to tee 3 and some will also take the more complicated route, backwards through rads up, forward through rads down and back to tee 3. We will call that ar2
With check valve in place and t.rail on ar1 is operating.
When ar1 is in operation, the check valve opens and therefore is no longer a check valve so ar2 comes into play and shuts the check valve so back to ar1 etc.etc

 

[fixitflav]

This is tee 3 at the top of the boiler, 22mm coming through the ceiling is the combined cylinder and upstairs return from tee 1, at this point we are about 4m downstream of the cylinder.

Tee 3 centre joins this with the 22mm return from the downstairs rads and the bottom of the tee goes into the the boiler return via the Spirotrap.

Boiler feed - is that the boiler flow?
Is that the pump - pumped return system? Never seen one like that but I'm just a DIYer. Or some sort of filter?

A pic showing more of the surroundings would help. If there's room maybe the up and downstairs returns could be commoned some distance away, giving room to tee in the cylinder return before the pump.

Looks like a 45° elbow after Tee 3. Is it possible to change to a 90° and connect to a tee on the pump inlet, with the cylinder return into the tee? Or is what looks like blockwork in the way? Fiddly job and need to remove temporarily the "boiler feed" pipe to do it.

 

[woodpeckerx]

With your check valve in place this is as expected.
If you fit a check valve to t.rail circuit all should be well but t.rail will then only come on with heating.

With CH on and towel rail still off, the check valve in the upstairs return is still chattering at times, is that likely to stop if change the towel rail to be always on?