Stopping hot water supply off a h/w tank

[Clive]

Hi,

I had to change a cold water tap on a "vanity" sink about 6 months ago. I remembered how to isolate the supply from the loft header tank - all went well.

I want to replace the other, plastic 30-year-old tap on the hot water side before it too fails.

Now the challenge is to stop the hot water supply. Maddeningly there is no stop-c*ck or valve on the hot outlet from the hot water tank. There is no isolator / ball-o-fix type valve below the sink tap.

I have been told by a guy, who came to clear the gutters, to do the following to change the hot tap. He suggested: just stop the cold supply to the hot water tank then drain the hot water from the tank. Then cut the pipe supplying the old hot water tap. Fit on a compression ball-o-fix to the cut pipe. Then attach a flexible pipe with screw attachments to the ball-o-fix and the new tap at the other end. Then refill the tank with cold and get rid of airlocks.

I would like to check this with you people. Is this the right way to go or should I approach this in a different way?

Thanks

Clive

[Nigel Molesworth]

Then change the tap.

[Christian McArdle]

Yes.

No. No need whatsoever to drain the cylinder. Just open up the tap, which will deposit a litre or two of water before stopping. The cylinder stays full.

Yes, although use fixed pipework rather than flexibles if appearance is of importance. You can insert the isolation valve into preexisting pipework by just cutting the right length of section out of it where it is straight.

Don't cut the pipework with a hacksaw. Use one of these:

Automatic Pipe Cutter (# 60976)

Christian.

[manatbandq]

That's why he's cleaning gutters and not doing plumbing. The hot water cylinder will not drain if you close off the inlet - try it, close the inlet and open a hot tap and see how much water comes out.

Now get a drinking, straw suck some water through it until it's full, put your tongue over the end and remove the other end from the water. Does the straw empty? No, it's like your hot cylinder full of water but no way for the water to escape.

You don't need to drain the cylinder, anyway. Just turn off the inlet to the cyclinder, open the tap you want to change and open a hot tap downstairs to drain the pipe work.

If you did want to drain the cylinder you would have to turn off the supply to the cold water header tank then open the hot taps to drain both the hot and cold tanks. This works because the cold tank is open to the air pressure and can drain.

MBQ

[Nigel Molesworth]

My thoughts entirely.

[Geoffrey]

That's all you need to do. Forget the rest. If the hot water tank isn't getting a feed the hot water will stop.

We changed the taps in our bathroom today. I can promise you it works.

[Set Square]

Thankyou - but I imagine that most regular visitors to this NG will already be well aware of that.

[Geoffrey]

Clearly not the OP. Perhaps you would prefer this?

Most of the regular visitors to this newsgroup know how to change a tap so even though we all know the guy who came to clear your gutters is talking complete bollocks we have no interest in giving you confidence in the methods WE eschew because we expect you to treat us with Godlike Respect and take all we say as Gospel.

I hope this response keeps Mr DIY a little happier, sorry for the inconvenience.

PS Bathroom revamp now 95% complete after only 2 months! Looks pretty damn good if I do say it myself and much of it thanks to the sympathetic and knowledgeable posts and responses of our regular contributers.

[Set Square]

I obviously hit a raw nerve! The point is that the question of how to isolate a hot tap with the least effort (and without needing to drain anything) had already been done to death in *this* thread - let alone in many others where it has been discussed.

It may perhaps be worth adding that if there isn't a gate valve in the feed pipe which runs from the bottom of the cold header to the bottom of the hot cylinder, a cork inserted in the outlet from inside the cold header works just a well - as long as you remember to remove it when you've finished.

[Nigel Molesworth]

I've found that most of my DIY projects follow the same curve as radioactive decay. In the first month it is 50% done, the next month

75%, then 87%, then 94%, 97%, 98%, 99%, 99.5%, 99.75% ...

Never quite gets to 100%

[John Stumbles]

Actually the analogy is more like this:

Get a teapot and pour water into it through the spout until it's full to overflowing at the top. Stop pouring. Does the teapot empty? No, it's like your hot water cylinder full of water but no way for the water to escape.

Bzzt! You just need to turn of the feed valve as before and drain the cylinder from the drain c*ck at the bottom. Air will enter the top of the cylinder from the vent pipe to allow the water to escape.

Actually you may still want to drain or stop off the outlet from the header tank because the gate valves usually fitted to the supply pipe tend to let by even when fully closed (if they work at all). I usually replace then with full bore lever ball valves.