One for the plumbers out there

[E-bmw]

I am currently re-plumbing the full central heating circuit of our house to remove the micro-bore and have a question.

Why is there a 15mm gate valve between the supply & return UNDER the floorboards?

Is it to aid quick filling/draining or commissioning?

I ask because as it was below the (chipboard) floorboards it wasn't actually accessible, and am wondering if it is needed.

[Mr Pointy]

If all the radiators have TRVs & there is no towel rail it may be a bypass circuit in case all the TRVs close at the same time.

[Gone fishing]

Are you sure its a simple gate valve and not a bypass valve? Its probably to allow water to recirculate when all the radiators are turned off..

If it is just a gate valve and you open it fully you'll find nothing gets warm, Close it fully and you have no bypass and the pump won't thank you when the valves are all shut. A proper bypass valve is more expensive but if you're doing the work it would be worth fitting one.

[JoshSm]

A 15mm gate is never going to flow enough to stop everything else working but it's a clunky way to do it compared to the traditional way like using a towel rail for that job or having a proper pressure controlled bypass.

Big issue with anything in a heating system is it getting blocked over time which is why a simple option like an open loop via a towel rail is the easy option as it's the least likely to fail.

Does seem a bit odd and unnecessary to bury it under the floor whatever it's trying to do though.

[E-bmw]

Thanks all, it makes sense that all are saying basically the same in one way or another.

I will be making the bathroom an open loop so it sounds like I don't need to refit it.

[g7jtk]

If you are replacing the whole system and boiler then any bypass would be fitted elsewhere on the system.