Combi - What's this valve for?

18 Sep 2005
Reaction score
United Kingdom
Just below my Voker combi, on the 22mm CH flow & retun pipes, there is a 'T' on each pipe linking both pipes together via a 15mm gate valve. To describe it electrically; it's like a short circuit between the CH flow & return pipes with a gate valve in the middle.

The gate valve is neither fully open or closed. Is this correct? What is the purpose of this?

Thanks in advance.
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Its a bypass to help get rid of heat after the burner shuts down and pump runs for a time after heating has been on
Its a cheap bodge to avoid buying the proper auto bypass valve. Its only really needed if you have TRVs on all rads or two port valves.

It should be set so that there is just a very small flow through it. Thats best done by starting from cold with it closed and opening it until warmth is felt on the return side.

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