Reverse circulation or not?

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Here is a rough idea of the pipework layout:



When downstairs is off the flow which is common to both acts as a one pipe system for downstairs. If a non return valve could be introduced to the flow pipe in the second and subsequent radiators on the system then all should be ok...in theory.
 
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And this is what I think may be happening :



What do you guys think?
 
That can't be, as you have no path for reverse circulation.

What must be happening is you are getting a gravity circulation into the rads, similar to a one pipe circuit.

The only way you would stop that is to cap the flow after the last downstairs rad, and run the new flow for the upstairs rads and connect somewhere around the same place as the zone valves.
 
Yup I agree it is a one pipe system. And I'm thinking if I screw a 15mm showerhose non return valve into the second and subsequent rads then It has to stop!
 
Yup I agree it is a one pipe system. And I'm thinking if I screw a 15mm showerhose non return valve into the second and subsequent rads then It has to stop!

It isn't a one pipe pipe system, and you can fit as many non return valves as you like, you wont stop parastatic circulation, unless you also stop wanted circulation as well.
 
Im listening, can you explain if its a one pipe why all rads dont heat?
 
It isn't a one pipe.

The heat is dribbling into each rad.

If you feel all the flows they will be hotter than the returns. Assumes you drawing is correct.

Also feel the return pipe prior to the zone valve for the ground floor circuit.
 
Cheers. Must call to inspect tomorrow. Open both zones and check flow direction. Then shut downstairs and see if flow reverses.
 
Do the checks in my last post. Do the checks first before the pipework gets hot. then compare it with both zones open.

As a crazy thought is there a by-pass anywhere not shown on the drawing.
 

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