Automatic bypass valve

26 Nov 2010
Reaction score
United Kingdom
When only the HW is selected the CH 2 way valve is correctly closed and HW open. However the radiators upstairs get warm with the heat coming from the return pipes. So, in summer we turn off the TRVs on the rads.

The manual bypass is 1 turn open, and you can feel the pipe below the bypass getting hot when CH is on - would replacing the manual bypass with an automatic bypass help stop this?

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It sounds as though you have reverse circulation

From the boiler on the return you should have in this order

By- pass

Cylinder return

Heating return

The bypass is often teed into the cylinder return in the airing cupboard and this is now technically the last tee.
From your drawing I would say the fault lies with the location of the Towel Rail Return, it should be the other side of the return from the cylinder

Try turning off the towel rail valves and see what the result is - my guess is the the problem will go away meaning the cure will be to fit a non-return valve to towel rail return or re-locate it to the correct position ;)

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