Hot supply sputtering / gate valves

[lister]

Hi folks,

I had to change a sink today with no isolation valves on the taps, so I had to shut off the water.

First turned cold off at rising main.

Looked in airing cupboard to be confronted by one tap like valve just like the rising main, and three red wheel valves (gate valves?).

Couldn't work out which one stopped the hot, so turned em all off, and ran a lot of hot taps until they slowed to a stop. All hunkey dorey.

After cutting the tap feed pipes, I was half way through fitting some isolation valves when there was some ominous gurgling in the system and a second later I got a four foot jet of water out of the hot pipe! This cycle then kept occurring approx every 30 seconds or so while I battled to fit the isolator!

After new sink in place I turned everything back on again. The problem I now have is that the hot feed is spluttering / low pressure from most hot taps in the house. Sometimes it's normal, sometimes it slows to a trickle. I assume I have air in the system.

My questions therefore are:

1) If I leave the hot taps running will they sort themselves out?

2) Can I have gotten air in the cylinder? It is dangerous to turn the cylinder on to heat if this is the case? Is there any way to tell?

3) The red gate valves don't seem to turn very far (maybe half a turn). Is this right or have I knackered em?

Many thanks, Lister

[Spamlet]

There should be a vent pipe in the top of the cylinder running up to overflow to the tank in the loft (assuming we are talking about traditional house and system: I bow to other writers if not.), so air should work its way out that way. If your pipes run a particularly circuitous route you may have more trouble getting the air out. Sometimes there may be enough play for you to shake the pipes a bit *with all the taps *turned off**, then you may be lucky and hear the glugs in the tank as the bubbles work their way up and out. If you try this with the taps on, the bubble will try to travel down, but probably end up staying still.

The gate valves:

should have several turns on them and they are very often stuck. They are meant to be fully open or fully closed. Sounds like yours were only partly open, and are now covered in crud. If not fully open they can rattle - until crudded at any rate -, but if turned out hard they get stuck, and commonly the end snaps off next time you try to close them. They are very prone to getting stuck and leaking yet very cheap to buy at your local plumbing suppliers.

What you should do is get yourself some new gate valves. Tie up the ball valve on the loft tank - bungees are good for this - (especially if the inlet has another stuck gate valve for the cold supply: if you need to replace that one you will have to turn off the cold supply further back.), and open all your hot taps until they stop, and leave them open for any water that is suddenly released when you start replacing the valves. If you have an old system you may have hassles replacing imperial sizes with metric, in which case you may find it easier to replace the lengths of pipe that have the valves in rather than trying to bodge old to new. If you have managed to change a sink, you should be able to change these valves without too much trouble - though working in confined cupboards full of pipes can always present you with them! (Start with the highest valve to minimise any spills.)

S

[Tim Watts]

Hi,

lister wibbled on Tuesday 10 August 2010 22:29

Yes, almost certainly gate valves.

Assuming a vented system:

The gate valve will *probably* have either stopped the cold tank filling (and thus indirectly the hot tank) or it cut the feel from the cold to the hot tank.

So, it sounds as if some air managed to get in and defeat the partiation vacuum that was otherwise stopping the water coming out.

Vented or unvented system?

If vented, it will fix itself. Unvented, no idea.

I thought they turned more than that - TBH used ball valves for so long, I've forgotton.

BTW - next time,shut off the rising main, leave everything else open and drain the HW tank via the lowest tap. Or get a pipe freeze kit :)

[Chris J Dixon]

Which is perhaps just as well, since you could otherwise have collapsed your hot tank!

Chris

[lister]

Many thanks for all your replies guys. After reading that I had another fiddle with the gate valves and managed to get the one controlling the cold water feed to the cylinder all the way open. All hot taps instantly fine again. Makes sense because they ran fine for a few moments this morning before spluttering again which I guess is due to the cylinder having a chance to fill full again overnight.

Looks like I'll have to look at replacing them at some point. Thanks again.

[lister]

Sorry, can you eloborate just for my future safety! How can I collapse the tank on a vented system?

[Dave Liquorice]

Yes, bastard things.

Not *fully* open, that is a guaranteed way for the crud/corrosion to jam 'em up very firmly. You stand slightly more chance of them not jamming if you fully open then close them half a turn or so. Also it's a good idea to fully close and reopen them every so often, like once a year.

If I ever take any of the gate valves out here they will be replaced with full bore ball valves. Note "full bore", most ball valves are not full bore and will restrict the flow, gate valves are full bore.

[Dave]

The advice on opening a valve fully and then closing it slightly applies to any type of valve. If you can turn it, you know it is open, if you can't, then you know it is closed.

Dave

[Spamlet]

Yes, sorry, I was going to mention they needed to be backed off a fracton: but not so much they get into the flow.

Cheers S

[Spamlet]

Many thanks for all your replies guys. After reading that I had another fiddle with the gate valves and managed to get the one controlling the cold water feed to the cylinder all the way open. All hot taps instantly fine again. Makes sense because they ran fine for a few moments this morning before spluttering again which I guess is due to the cylinder having a chance to fill full again overnight.

Looks like I'll have to look at replacing them at some point. Thanks again.

Watch out for crud in your taps if you let the cold tank right down - there may have been stuff floating on it. Probably won't happen but if your tank isn't fully covered you never know (I once got a CH pump choked with polystyrene beads, when its header tank ran dry that had been covered with a polystyrene sheet that had started to break up.)

[Spamlet]

Good idea Harry: must try to remember that.

S