hot water cylinder problem ?

[chris]

Hi, I have a problem whereby my cold water tank in the loft is constantly overflowing but this is not down to the cold water feed.

It appears to be due to the fact that the water is coming via the vent from the hot water cylinder straight into the tank and out of the overflow. The water in the "cold water tank" is alo warm.

No heating or hot water heating is running or has been for some time and has the boiler heating the hot water has been off some time so it doesn't appear to be the fact that the water is boiling in the cylinder.

The only way to stop it is to turn the stop c*ck off.

Any ideas what might be at fault ?

The heating system is a sealed/pressurised one with a traditional cold water feed..

Many Thanks Chris

[chris]

Just to clarify the water is coming in not via teh vent from teh hot wate rcylinder but via the hot water cylinder feed...i..e I think it being pushed up into the tank from teh hot water cylinder

[EricP]

Do you have an immersion heater with a busted thermostat?

[Wingedcat]

For some reason the water in the hot water tank is at a higher pressure than the water in the header tank. How could this be happening? Two likely causes:

1. There is some weird anomoly in your household plumbing where mains cold water is being fed up the hot water supply - perhaps due to a newly-installed mixer tap or shower.
2. The heat exchanger coil in the HW tank has got ruptured due to limescale attack over several years and is now leaking into the HW, as it is under greater pressure than the water in the tank. I take it you have a sealed pressurised heating system? This is also possible using open vented but would only manifest itself if the top level of the feed/expansion tank was higher than the top level of the HW Expansion tank. And it would also occur more slowly.

Others may suggest other causes but these are the first two that spring to mind.

Luke

[chris]

Problem due to mixer tap forcing mains water into hot water cylinder!

[chris]

Thanks Luke - you were right as regards the mixer taps,

We have one of those kitchen mixers with both a tap outlet and a spray outlet. If you have the temperature control lever set in between hot and cold, turn it on for spray but don't release the pressure ( controlled by a secondary lever) water starts flowing up the hot water pipe from teh mains!

Thanks for your suggestion

[adder1969]

There should be a non-return valve fitted to avoid that problem. I think it's a regulation and that's why some of the mixer taps don't really mix but give you hot and cold water at the same time, if you know what I mean.

[Christian McArdle]

Yes. The current installation is against the law. It is not permitted to have a mixer tap with mixed mains/gravity operation, unless it has double check valves, or is a concentric spout (i.e. not really a mixer at all).

Good luck with the check valves. If the hot flow was bad before...

Christian.