Gate Valve in CH Flow/Return Loop

9 Jun 2021
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United Kingdom
I’ve recently moved into a bungalow with an open vented central heating system installed in 1987 with 8mm microbore running to the 10 radiators.

I’m intending to replace the microbore and whilst I was crawling around under the floor I found a gate valve in the 22mm flow/return loop, the purpose of which I don’t understand. I think it’s for balancing the system, but I’m not sure.

A rough plan of the layout is attached, radiators and HWC removed for clarity. The airing cupboard pipework at the bottom is an elevation view, the underfloor CH loop at the top is a plan view. The flow/return from the boiler via the loft are 28mm, reducing to 22mm after the bypass gate valve and then it’s all 22mm underfloor with manifolds and tees reducing to 8mm for the rads and 15mm for the drain.

The floor standing LPG boiler is in a small WC at the back door with a cupboard built around both it and the pipework. The flow and return go straight up into the loft, I’ve not drawn it out but the return is just a clear run from boiler to airing cupboard, the flow has tees for the vent (pretty much as soon as it comes up from the boiler) and for the cold water feed from the F+E tank (about a metre before it drops down into the airing cupboard).

1) the gate valve in the airing cupboard between 28mm flow and return is, I think, a manual bypass valve. It’s currently closed, can it be left like that?
2) is the gate valve underfloor between CH 22mm flow and return for balancing the system as I suspect?
3) it’s currently about 1/2 a turn open, I know it’ll need adjusting after the radiator pipework is replaced if it is a balancing valve, but if it’s not can it just be shut or removed completely?
4) there’s nowhere near the boiler that’s accessible are there any issues with putting a system filter in the 28mm return pipework in the airing cupboard?

Thanks in advance, if you need more information let me know. I posted this elsewhere with other information but that’s effectively degenerated into a 15mm copper vs 10mm plastic debate and I still don’t know what the gate valve under the floor might be for.

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