Reverse circulation in 2 zones installation

[Ant1]

I created an central heating installation with 2 zones as shown in the diagram below.

Zone 1 is for the ground floor while zone 2 is for the first floor. The return pipe from zone 2 merges with the one from zone 1 through a tee when reaching the ground floor.

The issue I have is when I activate zone 2 only, some of the radiators from zone 1 heat up too as shown in the diagram below (highlighted in yellow):

I believe this is happening due to reverse circulation on the return pipe after the tee, as shown with the blue dotted arrows.

I believe I have 2 options to address the issue.

Option 1: installing a check valve at the location shown in the next diagram

Option 2: running the return pipe for zone 2 all the way back to the boiler as shown below

Which option would you use?

Option 1 is obviously the cheapest and quickest, but is there any advantage / inconvenient using either option?

Thanks!

 

[cross thread]

Run it back to the boiler

 

[Exedon]

As above back to the boiler slightest bit of crap in system = non return valve jammed open.

 

[ericmark]

I had a similar problem, I did not expect it with micro bore. I fitted electronic TRV heads, not for that reason, but it stopped the problem.

 

[Ant1]

Thanks guys, since it is not a long run I will extend the return pipe for zone 2 all the way back to the boiler, I did not think about the possibility of the non-return valve getting jammed.

 

[fixitflav]

Thanks guys, since it is not a long run I will extend the return pipe for zone 2 all the way back to the boiler, I did not think about the possibility of the non-return valve getting jammed.

Do you also have a HW cylinder fed from the boiler? If so, make sure the return from that comes in after the 2 heating zone returns are commoned.

 

[Ant1]

Do you also have a HW cylinder fed from the boiler? If so, make sure the return from that comes in after the 2 heating zone returns are commoned.

No HW cylinder as this is a combi boiler but thanks for flagging it, useful to know.

 

[Terrywookfit]

No Need to pipe to boiler. It will be fine into return after last rad.

 

[SpecialK]

How hot are the rads that are not meant to be on? Is the pipe next to the off zone valve getting hot?
Very odd as it works fine one mine - Although I have the zone valves on the returns...

 

[Terrywookfit]

Each zone must be piped from the common flow and return to prevent reverse circulation.

Its not fookin difficult to remember.

 

[Ant1]

How hot are the rads that are not meant to be on?

Pretty hot actually, the hot water definitely comes from the return pipe.

Is the pipe next to the off zone valve getting hot?

The flow pipe on zone 1 valve is not getting hot; this would suggest the diagnosis I made in my original post is correct.

 

[Ant1]

Each zone must be piped from the common flow and return to prevent reverse circulation.

Its not fookin difficult to remember.

Well I came through many diagrams showing this kind of set-up and obviously I wrongly thought it was acceptable. Note that this is my own installation in my own house, not being a plumber I just wanted reassurance that the diagnosis I made in my original post was correct, thanks for confirming this.

 

[SpecialK]

Why is there no "reverse circulation" in the first two rads?
Are you sure you don't have a bypass valve or something you don't know about messing things up and connecting loops.

As I commented before my setup is very similar. I only have the rads heating up that the zone valve is open on...

If you isolate the rads one at a time - does this solve the problem when one is isolated? I'm wondering if one joins to the other loop somehow?

Anyway - not a plumber so maybe I'm totally wrong....

Well I came through many diagrams showing this kind of set-up and obviously I wrongly thought it was acceptable. Note that this is my own installation in my own house, not being a plumber I just wanted reassurance that the diagnosis I made in my original post was correct, thanks for confirming this.

 

[fixitflav]

Anyway - not a plumber so maybe I'm totally wrong....

I'm not a plumber either, but I still think that's wrong. There is only a problem if the water has 2 parallel paths to return to the boiler.
The OP's diagram with the flow arrows doesn't tell the whole story. IMO when Zone 2 only is on, the water flows the "wrong" way through the 4 Zone 1 rads to the left of the tee, then through the other 2 the right way, then back to the boiler.

 

[Ant1]

Problem all fixed after using option 2 in my original post, never expected reverse circulation but learned a new thing.