Hot water spluttering - air in pipes?

Hi,
Two of the three hot water taps in my house splutter then die then come back into like again in a continuous cycle within a few tens of seconds of running them.
I have tried blasting cold water through the hot tap using a hose, and this relieved the problem for a few minutes, but then it returned.
The header tank has enough water in it to feed the cylinder throughout.
Could air be getting into the pipes somehow?
A bit about the system:
I have a hot water cyclinder on the first floor with a header tank directly above it - the two are combined as a single unit.
There is loads of scale in the header tank, but the pipe that connects the two appears clear.
A 15mm pipe from the cyclinder runs to the ground floor where it supplies three taps and a washing machine.
The kitchen sink tap is supplied via a narrower guage pipe (<15mm), and works ok, although the flow is quite puny.
The bathroom sink tap is a 15mm tap and has the problem - this tap is supplied via a rise in pipework of 2 - 3 feet.
The bath tap is a 22mm tap and also has the problem - this tap is supplied via a rise in pipework of about 1 1/2 feet.
I haven't checked whether the washing machine point has the problem or not.
When the affected taps are opened part way, this does eliminent the problem but the flow is unsatisfactory.
I have had the problem since moving in.
Any advice would be much appreciated!
Cheers Dan
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I would surmise that the hot water tank isn't being filled quickly enough by the header tank to sustain the flow rate of the taps so the blockage must be in the pipework between the two.
Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though.
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by
be in

Thanks Dave - I'll investigate this further...
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Hello Dan

Try dropping the temperature of your HW cylinder and seeing if that makes a difference.
--
Simon Avery, Dartmoor, UK
uk.d-i-y FAQ: http://www.diyfaq.org.uk /
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I had the same kind of problem a while ago. I also live in a hard water area. I got to the root of the problem when I had to replace the hot water cylinder because of a leak . On removing the old cylinder I was amazed at the amount of scale that had built up over a few years. It was not just deposited on the interior surfaces of the cylinder, there was loose sludge filling nearly half of it ! At a high rate of flow the sludge was disturbed sufficiently to cause the spluttering and glugging.
Richard.
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On Mon, 8 Dec 2003 11:28:19 +0000 (UTC), Dan Winchester wrote:

The air released by the heating of the water has to go somewhere, it rises to the top of the HW cylinder. In a normal doomed top cylinder it simply goes straight up the vent pipe. or will do on a properly installed vent pipe...
With yours though it must collect at the top of the HW part. ISTR when I had one of these combined thingies there was the equivalent of a vent pipe that went from the top of the HW part to above the water line in of the CW part. Is that clear? If not the air released only has one way to go out through the taps. Well it's a theory, a theory that is mine, mine that theory is...
--
Cheers snipped-for-privacy@howhill.com
Dave. pam is missing e-mail
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Hi Dan,
I live in a soft water area (Ayrshire, about 30 miles south of Glasgow) hence scale build up is unlikely.
My tank did the same "spluttering" as you have described. The problem was that the cold feed was 22mm from the cold tank some eight feet directly above the hot tank. But the hot tank output then came back up into the loft and along then down to feed the rest
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How come this blinking stoopid newsgroup reader SENDS a half-composed reply before I get a chance to finish it?!
Anyways, as I was saying.... (apologies):

down
... of the hot water needs in the house. As you ran the bath the water would surge for 4 or 5 seconds, then slow then "gulp" then back to surge again.
Methinks the demand from the tap was enough to (somehow) overwhelm the 22mm supply from the cold tank, hence water was being drained from the expansion pipe until the cold tank got a chance to replenish the hot somewhat and then the cycle repeated.
About 2 years ago I relocated the tank (for other reasons, all documented on this newsgroup) and at the same time I reworked the supply and the other pipework. The feed was changed to a healthy 28mm; so was the draw-off from the top of the tank. The route from the top of the hot tank to the eaves distribution was only a drop of three feet (or so), still in 28mm pipe - no reroutes back up through the upstairs ceiling (via the loft).
Result: no gulping at the bath tap - just a solid stream of hot water.
And a smug look on my face knowing that I've fixed this problem :-)
Mungo recommends that you investigate the girth of yer pipes and the topology of the hot water outlet.
HTH
Mungo ;-)
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Thanks everyone who responded.
I think the problem lies with supply of water from the header tank to the cyclinder, as suggested by Dave and Richard - either the supply pipe is scaled up, or it supplies into a layer of scale in the bottom of the tank above the bottom of the pipe.
I might try some Fernox DS3, although a plumber friend has told me to avoid this and replace the tank as DS3 could expose leaks currently sealed with scale and generally gunk up the system.
Cheers Dan

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On Wed, 10 Dec 2003 13:04:13 +0000 (UTC), "Dan Winchester"

I think that he's probably right. By the time you've bought the chemical and spent quite a lot of time on it, and as the plumber says, more than likely created other problems, it's going to be quicker and probably cheaper to replace the cylinder.
If the water is exceptionally hard, you could consider installing an ion exchange water softener. This will prevent scaling completely, and you can more than cover the cost of the salt to regenerate it in the savings in shampoo and detergents, let alone the capital cost of the water heating equipment..
.andy
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wrote:

avoid
Yep, he recommended adding some sort of softener, at least to the cold feed into the hot water header tank.
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It isn't a major task to remove and check the supply pipe. If that's clear then it might be worth removing the immersion heater from the tank (or the blanking cap if there is none), sticking a wet and dry vacuum cleaner pipe down inside and hoovering out any loose crap in the bottom. With both of these done I'm sure your problem will be resolved.
Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though.
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