Valve from heat exchange

[Beasty1711]

Hi,

I’ve just moved into a new house and a bit confused by some of the valves in the airing cupboard.. mainly this red handled one.
I had to shut the hot water off so mistakenly closed it, however I then realised that it want water but central heating related.


My question is
1. What is it for?
2. How open / closed should it be? I had a property years ago where there was a similar tap that when fully open or closed wouldn’t heat the downstairs radiators.


Thanks
Pete

 

[dilalio]

It’s ‘very likely’ to be a manual bypass for your CH flow and return. Should be opened just a crack, to allow system water to return to the boiler if all rads are shut down and creating high resistance (or completely closing circuit).
Open it too much and system water will take the path of least resistance, back to the boiler and starve furthest rads from receiving heat.

 

[Beasty1711]

Cool thanks.. will close it off a bit later

 

[Hot&Cold]

If they have not been turned for a few years can leak water.

Be prepared