Why are my flow and return pipes connected?

23 Oct 2007
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United Kingdom

I am trying to understand my pipework coming from my boiler and it seems pretty straight forward, mains water in, hot water out to the taps etc, and a single flow and return to the radiators, the return has the word return written on it in pen.

My question is why are they connected? I have put the heating on and the connecting pipe gets hot straight away so is definitely connected.

Any explanation appreciated.

Picture of the pipes attached.




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Hi Motman, For what purpose? The pipe has an isolation valve half way that you can see in the pic, this seems to be open as it gets hot on the right hand side straight away.

Should this be like this? Is it going to be causing anything like the system being inefficient, or 'thinking' the rads are up to temp when they are not?


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If it makes any difference its an external oil fired boiler. thanks.
It should have an auto bypass valve in there, not a crusty old ballofix
Does it make it any better if it's a gate valve (like mine is)? Always thought it odd, and otherwise professionally installed system.
ha ha, so are you saying it should not be linked? Thanks.

There should be a bypass somewhere on the system, between flow and return, that allows system water to circulate if other route is restricted/closed, ie rads have TRVs which have been satisfied and shut down or motorised valve has closed and the system needs somewhere for the pump to send water to cool down, during overrun period.

However, the bypass (link) should have either a automatic bypass valve installed on it or a properly set gate valve.

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