CH zones

[Stephen]

Hello,

I was wondering about isolating central heating zones. Say you wanted to remove the upstairs rads to decorate, could you still run the downstairs zone?

The plumbing would be boiler to pump to valve to zone. At first I thought that if the valve was closed, you could drain down a zone and continue to run the others.

However, I then thought that although the "start" of the zone might be isolated, the "end" is not, after all, all the returns all join together at the boiler. Would a drained zone backfill?

Then I thought some more and thought that it would not backfill because the air in the empty pipes could not be displaced.

I don't want to try it and find out the hard way! So can you tell me, can you isolate a zone just at the motorised valve or do you also need a full bore valve on the return?

I'm thinking the downstairs zone, being below the level of the upstairs CH and HW cylinder, might be particularly susceptible to backfilling?

Thanks, Stephen.

[David Hansen]

On Sat, 01 Nov 2008 13:58:15 GMT someone who may be Stephen wrote this:-

No.

Once in a while you may be lucky, but at the most inappropriate moment air will get in and the contents drain out.

Valves are needed on flow and return.

Do think through the motorised valves though. Why do you want them? For zoning a building north and south are better. If all bedrooms are upstairs then ground and first floor could be set for different times, with thermostatic valves to deal with overheating on the south side.

[www.GymRatZ.co.uk]

What's stopping you just turning off the lockshield vale at one (or both) ends or if thermostatic valve just remove the thermostatic top and screw down the caps to keep valve tight shut. Then just remove/decorate/refit/refill rads on a room-by-room basis.

You couldn't just shut off one end of the upstairs circuit as the return flow to the boiler is still going to be presurised.

Perhaps I didn't understand the scenario correctly, but that's how I'd do it whether zoned or not.

Pete

[Andrew Gabriel]

When I designed my heating system, I included provision to isolate each of the main pipework branches (which roughly correspond to the zones, but not exactly so). I used full-bore lever valves in the flow and return. This does allow for keeping the rest of the system operating. It was quite essential as I didn't finish the main downstairs branch until 6 months after the heating was switched on!

Something else I did was to design the pipework layout so it all slopes downwards towards the drain points, so in theory I can drain it down and end up with nothing in the pipework. Never needed to drain it down yet though.

[John]

Some of those concepts should be mandatory in new builds.

[ransley]

It depends on how its plummed in, there are several designs.

[ARWadsworth]

They should be, but have you tried to make plastic pipe slope? (new builds seldom use copper)

Adam

[Stephen]

I am about to re-do the CH plumbing and was just thinking about adding isolation valves "just in case" and redecorating was the first example that came to mind. I agree that to decorate you probably only need to isolate one rad at a time, rather than one zone, and it was a bad example. Andrew gave a better example where he ran part of his heating whilst still working on the other half.

I may still add the valves. I think it's better to have them and not use them rather than wish I had fitted them and want to use them!

Thanks, Stephen.