Is this an isolation valve?

I'm getting a small leak (the occasional drip) from the tap on an isolation valve which is part of the top-up for the CH system.

The top-up is a simple flexible connection with an obvious isolation valve with handle on one side and something which looks like an isolation valve but has a hex nut where I would expect a slotted screwdriver fitting or a handle.

A quick check shows that the hex nut will go through more than a quarter turn and is currently turned as far clockwise as it will go. I'm wary of turning it too far anti-clockwise just in case it's going to come unscrewed, fall out and coverthe floor in water

Here's a photo of the set up

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offending item is on the left - here's a close up photo
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've had a quick look through various web-sites but I've not come across an isolating valve looking like this.

Can someone enlighten me please - if I turn the nut fully anti-clockwise will it shut off the system or will it just fall out?

Alan

Reply to
Alan
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It's a double check valve.

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would not turn the nut fully anti-clockwise.

Reply to
ARWadsworth

So IIUC, this is what I think of as a one-way valve so I can simply turn off the water supply and disconnect the leaking isolation valve and there won't be a back-flow of water from the double chweck valve end?

Alan

Reply to
Alan

Correct. You might find this helpful:

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Reply to
Andy Wade

The nut is designed to allow testing that both of the double check valves are working - there's one either side of it. It should be left tighened up normally, and should not leak.

The braided hose should not be left in place except when you're topping up the heating system. With the hose removed, no water should leak back out of that valve, and if you do undo that nut, no water should leak out of that either (save for an initial drip because the cavity it goes into will contain static water, but it shouldn't carry on dripping indefinitely). If the double check valve leaks from either point, it should be replaced. This can probably wait until you are next having the heating serviced - it's probably not an emergency unless it starts leaking fast. With the hose in place, it's not possible to say if the valve has failed of not, as it may be preventing enough pressure difference to fully shut off the double check valve.

IME, the guts of these valves are destroyed if they ever get frozen.

Reply to
Andrew Gabriel

Thanks,

Alan

Reply to
Alan

The double check valve lets water flow into the CH system from the mains, but prevents its return. So you could remove the flexible connection, and with the the tap closed on the right, no water will flow from either side.

Obviously you can't remove either valve from the fixed piping without water escaping since the valve is all that is holding it back.

Reply to
John Rumm

But he can turn off the mains cold water and then remove/replace the leaking isolation valve.

Reply to
ARWadsworth

Not sure which isolation valve you mean? In the original photo I can only see two valves; the tap on the right and the double check on the left unless I have missed something? You won't be able to take either of those off the pipework without getting wet! The only bit you can safely disconnect is the braided flexy connection.

Reply to
John Rumm

The tap on the right (with the handle) is the one I want to change. Now I'm told that the other (which I didn't recognise) is a non-return valve I can just shut off the water and disconnect it without the entire CH system draining onto the floor ;-)

Thanks to all

Alan

Reply to
Alan

The valve on the right (I assumed the one with the plastic tray underneath it catching the drips needed replacing). However the OP could have moved the tray for the photo!

Once the mains water stop tap is turned off, there is no reason why it cannot be removed and replaced (other than the standing water in the pipework if the cold taps in the house are not opened up)

The OP certainly cannot remove the double check valve without draining his radiators.

Reply to
ARWadsworth

Yup with all the focus on the double check valve, I assumed that was the one he wasted to replace.

Indeed - the key step being turning off the water! It sounded from earlier discussion like he wanted to swap out the tap without doing that.

Well once you have dropped the pressure a bit by draining a couple of litres, you can swap one tap for another with a quick thumb over the end shufty. Usually don't spill more than a cup full if you are quick.

Reply to
John Rumm

Yup, disconnect the flexy hose. The double check on the left will keep the water in the CH system. (you may spill half a cup out of the hose!)

The valve with the knob you can change once you have turned off the mains cold water. Again if you drop the pressure a bit at a tap, and then endure the other taps are off, you can do a quick swap like for like without draining everything down.

Reply to
John Rumm

Went to try changing the isolation valve (tap) - turned off the mains, checked no flow through taps and disconnected the flexible hose at the tap end - water poured out from the flexy hose :o

Fortunately I was paranoid enough to have been prepared (with plasic sheet and bowl) so no harm done.

Looks like the double check valve is also naff so now it's down to draining the system and replacing both valves :(

Alan

Reply to
Alan

Did you say something that rhymed with Clucking Bell when the water poured out?

Reply to
ARWadsworth

In article ,

Isn't that always the way.

To avoid this sort of problem my system has a 1/4 turn isolating valve on both the mains side and the C/H side.

Also, to make it easier to drain down the system and to inject inhibitor, I have an open port (via valve) on the system side and the check valve on the mains side (flipped to correct the orientation).

As you're draining down anyway this may be a sensible change to incorporate.

If you fancy a bigger chore, it may be time to shift the filling point, above that rad isn't the most inconspicuous spot.

Reply to
fred

Deep joy!

If you are feeling brave, leave the flexy connected at both ends, and undo to union nut for the double check valve, while keeping it pushed against its stub of pipe with the other hand. Once the nut is free, quickly swap the DC valve for a new one[1], and do the nut up again. As long as the CH is off, and you have bled a litre of water out of a rad somewhere, you won't lose much more.

Just make sure you have the replacement bits easily to hand and in the right state to use!

[1] Pull valve off, thumb over pipe end, pick up new valve and repeat. Push valve against pipe stub while tightening union nut.
Reply to
John Rumm

Actually it was more like Go Hit! :)

Reply to
Alan

Need to drain enough so pressure guage shows zero.

Reply to
Andrew Gabriel

Try to keep it so you are within line-of-sight of the pressure guage whilst filling system. Another option would be to add another pressure guage at the filling point.

Reply to
Andrew Gabriel

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