Another central heating draining question – just w ant to check before I do something terrible

[Clive]

Hi,

I want to move a hot water radiator. I have a ?conventional? DHW/ CH system with floor mounted boiler, expansion / header tank, two pumps and hot water cylinder.

I have read up on the method to drain the system and it seem straightforward. I just want to check if there are any gotchas or things I might have misunderstood.

1) Switch off the CH by switching timer control to off and setting all thermostats to lowest setting

2) Stop water supply into the header / expansion tank by tying off the ball c*ck with piece of wood and string

3) Fit a hose between the system drain tap and the drain gulley. Open the drain tap. Now this I'm a bit concerned about. Outside the front door, below the step is a drain tap. Now I am guessing this is the CH Drain as it is pretty much at the lowest point. in the whole system. Could it be something else? Is there any way I can check?

4) As the system drains work down from the top of the house opening the radiator bleed valves letting air in but closing the valve for a minute if water comes out.

5) Work down through the house opening each radiator bleed valve.

6) Wait until no more water comes out of the drain tap.

7) Put lots of old material under the CH pipe to be cut. Cut the pipe with one of those circular pipe cutters ? the one that fits the pipe not a ?universal? one with a screw adjustment. The reason for the ?dedicated? cutter is the cut will be clean and at right angles to the pipe. Some dirty water will come out of the pipe to be captured by the old material. Cut the other pipe in the same way.

8) Fit the new pipe. The old pipe is copper and I'm thinking of fitting some kind of ?flexible pipe? with those ?screw in? connecto rs rather than using compression joints and more copper. The reason for doing that is the flexible pipe will be easier to route and I need to put in less joints (I don't have a copper pipe bender). Anyone have an opinion on mixing copper and the flexible pipe? The new radiator position will be quite close to the old but copper pipe would require a few bends and joints that I want to avoid.

9) Connect up the rad wrapping all the threads using PTFE (?) tape.

10) Close the system drain tap and the rad bleed valves. Can/ should I put some chemical in the header tank to ?flush? the system? Then fill, empty and refill? My worry is the descaler will be corrosive and lots of little pin holes in joints will open up.

11) Whether I flush / descale or not, do I just put inhibitor in the header ./ expansion tank before I fill the system for the final time?

12) As the system fills I open and close the rad bleed valves from the bottom rad to the top until the rads are filled.

13) Check the new joints for water tightness.

14) Switch the system back on and check rads become hot.

15) Over the next few days bleed the rads again to release any dissolved air that has come out after system has filled?

Have I missed any steps or things I need to check?

Thanks,

Clive

[The Medway Handyman]

Turn the power to the boiler etc off.

Drain taps nearly always drip, take the oppourtunity to change the washer/o ring. Get someone to watch the water level in the tank while you undo the drain c*ck. Can't see it being much else. Water is likely to be black as well.

Yup. That water coming out will prolly be black & horrid! Lots of old material!

Not sure what you mean by flexible pipe. Post a link?

Never a bad idea to flush out. Fernox & Sentinel both do neutral non corrosive cleaners.

Seems like you've thought it through to me.

[Dave Plowman (News)]

Connect a mains pressure hose to the drain outlet and re-fill that way.

[Roger Mills]

If you really want to drain and flush the whole system, that's fine. But if the system has inhibitor in it and is fairly clean, and you just want to move one radiator, you don't need to do half of what you have listed above.

For a start, you don't need to drain any of the radiators other than the one boing moved. Turn off both valves on each rad, noting the position of the lockshields so that you can return them to the same state. If you have TRVs, remove the heads and fit decorating caps to hold them firmly shut. Bung up the supply pipe outlet in the F&E tank with a cork. Likewise the vent pipe.

Then drain the radiator to be moved by cracking the valve to rad joints and collecting the water in a shallow container (having first turned off both valves, as above). Once the rad is drained, fully undo both valve to rad connections and remove the radiator. In order to modify the pipework, you

*only* need to drain the pipes which connect to that rad - not the whole system. You can do that by opening each valve in turn and collecting the water until no more comes out. When it stops running, you can safely cut the pipe - but keep a drip tray under it in case any more comes out later. It would actually make sense to mount the radiator in its new position *before* breaking into the pipes - thus minimising the time when the pipes are open.

[Roger Mills]

Do *NOT* use a hacksaw! You'll end up with rough bits which will damage the seals in the fittings. You must cut the pipe cleanly and squarely. A sharp pair of garden bypass (not anvil) secateurs is a suitable alternative to the proper cutter if you only have a few cuts to make.

I would wait until you have finished your mods, and *then* drain down and refill with fresh water and inhibitor. Save about 10% of the inhibitor and pour it into the header (fill & expansion) tank after you've bled all the air out, and everything has settled down. Otherwise, it could take a while for inhibited water to get back into the F&E tank and you might get some fungal growth appearing.

[Clive]

For the money I have spent, I will buy the correct tool and not risk boogering up the joints. A slow leak and a fallen ceiling would work out much more expensive !!

Good, good point. Will do.

Cheers,

Clive

[Roger Mills]

It depends how they're actually connected. If the output of each rad is connected directly to the input of the next one - and nothing else - then the same flow rate necessarily goes through *all* rads, and there is no scope for balancing. In this case, if you turn one rad off, the flow stops to *all* of them.

It's more likely - if indeed it *is* a single pipe system (which are pretty rare these days) - that there's a pipe going right round and that the flow and return for each rad are tee'd off this pipe. In this case, you *can* turn a single rad off without the whole lot stopping, and you *can* balance. Balancing determines how much of the flow goes through each rad rather than through its by-pass pipe.

[Roger Mills]

Not really! My method involves making sure that each radiator stays full - which requires valves to be turned off *both* ends. If there's only one valve you can't do that! Exactly what sort of connection is at the non-valve end?

Your other post suggests that you may have a single-pipe system - in which case a lot of what I wrote may not apply. I was assuming a two-pipe system with 2 valves per radiator. Most of the water is contained by the radiators with a (relatively) small amount in the pipes. So if you can keep the water in the rads by closing both valves, and if you use corks to stop the F&E tank emptying, you don't have to drain *that* much out of the pipes. Once the water stops coming through an open valve, you can then remove the valve - or cut the pipe close to the valve - without getting a flood.

*Except* that you may get a bit of air gurgling round the system and allowing a drop more water to drain from further back - which is why I suggested using a drip tray.