Hot water has bubbles in it.

[Ian Stirling]

If the bath tap is turned on beyond what you might expect from a sink tap or so, it rapidly starts emitting large quantities of air as well as water. The only thing I can think of that might cause this are a rather big leak, which would have been obvious by now, or dissolved air coming out of solution. But there isn't that amount of air dissolved in water.

The bathroom is connected to the hot water cylinder with some 10m of 22mm pipe from the attic, and is around 4m above the bathroom.

Anyone have any clues?

[Christian McArdle]

My guess is that the the vent is probably being sucked dry. This often happen when you have a pump attached, but can also happen without a pump in bad cases. It is caused basically because your desired flow rate is above that which can be supplied by the connection between the cold tank and the hot water cylinder. When this happens, the water is taken from the vent pipe instead, which soon becomes empty and draws air.

This could happen because:

1. Cold feed valve not fully open or broken.
2. Hot water cylinder feed pipe underspecified, overly long or scaled up.
3. Cold water tank fill valve slow (so cold tank runs out)
4. Cold water tank undersized (so cold tank runs out)

To solve it, you need to do one of the following:

1. (Only in marginal cases) Fit a flange to the cylinder and take the water from there.
2. Upgrade the hot water cylinder cold water feed/fix or open dodgy valve/bigger cold tank
3. Install a mains pressure hot water system.

Christian.

[Ian Stirling]

I assume the important number is how far the

It's only around 1.5m long, and is 22mm (IIRC) I don't think there is a cold feed valve, I'll have to have a closer look.

I'd not have thought so, as it fills quite fast, and is fairly large. Something to check.

Would simply fitting a check valve to the vent tube work? Or is that a bad idea.

I'd rather not go down this route, as it doesn't bother me that much. Thanks, some things to investigate tonight.

[Christian McArdle]

That may result in death or serious injury to occupants of the property.

If the low flow rate doesn't bother you, turn down the bath tap isolating valve to prevent you drawing too much water.

Christian.

[Christian McArdle]

P.S. With the short 22mm run, I'd seriously suspect scaling at the bottom of the cylinder spreading into the feed pipe.

I'd seriously consider disconnecting the feed to have a look. If there is scaling, flush out the pipework and cylinder as much as is practical. If you find that it is really bad, consider replacing the cylinder. Gravity ones aren't expensive.

Christian.

[Ian Stirling]

I suppose that could be a bad thing. I suppose the concern would be that with an electric heater you'd get a boiler explosion. But for that to happen, the check valve would need to fail closed, the cold-water feed would need to block totally (or the valve be turned), the thermostat would need to fail and I'd need to be using electricity for some reason rather than gas. Unlikely. (not going to do this)

Another option.

Looking at all the facts, it does look like sediment building up and nearly covering the cold inlet pipe may be an option. The cold water tank has had an amazing amount of gunk in it when I cleaned it a while back.

I think I'll try closing the cold water feed valve, draining the cold water tank, attatching a wet-dry vacuum to the cold water feed line.

The worst that can happen is I end up with an interesting flat copper sculpture :)

[Lurch]

On Tue, 02 Mar 2004 17:28:31 GMT, in uk.d-i-y Ian Stirling strung together this:

Whatever the reasoning behind it you still can't fit any sort of vave\device to the vent pipe. I'm not sure whether you're thinking of it or not, your post isn't that clear, but just to make sure I thought I'd mention it. The other thing is the immersion heater would be used if the boiler breaks down. Not an everyday occurence but still possible. ..

SJW A.C.S. Ltd.

[Ian Stirling]

Can anyone think of a reason other than comedy value to have two valves in series within 18" of each other on the cold water feed pipe, with one cunningly hidden behind the loft insulation wrapped round the tank.

[Lurch]

On Tue, 02 Mar 2004 18:29:08 GMT, in uk.d-i-y Ian Stirling strung together this:

Because someone couldn't get to the hidden one so they put another more acessible one in? Am I right? Do I get a prize? ..

SJW A.C.S. Ltd.

[John Flax]

No-one has mentioned the possibility of air being sucked into the water because something is wrong in the region of the gland which seals the tap's spindle, e.g. limescale built up neat the bottom of the spindle distorting the gland thus allowing air to enter the stream of water. For illustrations etc see;

[Ian Stirling]

No. Both the valves seem to be fully open however, and closing and opening has not made any difference, nor attempting to suck out the debris with a wet/dry vac.

Yes! One shiny potato. Just paypal me the postage of 1 pound 50p, and it'll be speeding on its way to you.

[Lurch]

On Tue, 02 Mar 2004 19:06:36 GMT, in uk.d-i-y Ian Stirling strung together this:

Could they be remenants from a previous installation of shower or such like?

I'll think about that, I'll just go and check my potato collection see if there's any more room for shiny ones! ..

SJW A.C.S. Ltd.

[Ian Stirling]

Nope, it's one unbroken Z-shaped pipe, with a valve at either end, and a couple of elbows.