warm/hot water in cold water tank!

18 Sep 2004
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United Kingdom
hi guys, I've got a back boiler (vulcan verona 58) and from what I can make out it's an open vented system.
The problem is the header tank seems to be overflowing all the time, the water in the header tank is warm/hot, and the feed pipe from the header tank to the cylinder is hot. It seems to me hot water is coming up from the cylinder to the header tank?

any ideas gratefully received,and thanks in advance.

ps have changed ball valve, set to about 2" below overflow pipe, previous one dripping slightly
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Sounds like you have not allowed for water expansion when the system is running. Set your ball valve to cut flow when the water level is 100 mm from bottom of tank.
Do this when the system is cold. :D
Sounds more like the cylinder coil has gone.

are the water level in two tanks different heights
thanks for the reply, not sure if I made it clear but actually my cold water tank that's overflowing, tank about 300mm high, so no chance of setting the ball valve to 100mm from bottom of tank, will try setting it as low as possible though.
Is the water supposed to be warm though, the waters not coming from the vent pipe but up through the cold water feed.
Hopefully i'm worried about nothing?
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you have two tanks

A big one that feeds the cylinder.

A not so big one that feeds the heating.

Which one is overflowing and whats is the water height of the two tanks.

Is the one that over flowing lower than the one thats not.
its the big one that feeds the cylinder thats overflowing, both tanks the same height, lived in house for 2 years only recently started happening, nothings changed, no new pump etc.
The water levels should be the same but unlikely to be a problem.

You now need to check all your taps etc that has a shared mains cold with the hot.

Washing machine could be the first suspect, followed by the mixer taps on the kitchen sink.

To test the theory turn the mains cold off and observe if the overflowing slows and stops
I suspect that Doitall has this one cracked. There was somebody else on this forum a week or two ago with a similar problem.

To make fault finding easier look for a gate valve or stopcock in the cold feed - the pipe leading from the bottom of the cold tank to the bottom of the hot cylinder - and close it. If mains water is forcing its way into the hot system you will now get water coming out of your vent pipe. That's a lot easier to spot.

Now turn off the mains stopcock like Doitall says. Does that cure the problem? If so you have to look for a wrongly fitted mixer tap. The only mixer that should run on mains cold water is a kitchen sink mixer and, if you study these carefully, you'll see that they have two distinct exit holes. They aren't really mixers at all. Every washing machine I've ever fixed has had independent solenoid valves for hot and cold and they tip water straight into the open soap tray. But check anyway because some moron might have plumbed it in all wrong.

If water still comes out, turn off your CH pump (if it's running) to see if that stops the flow. If it does then your cylinder heating coil is leaking boiler water into the cylinder.

That question about tank heights is also significant. What matters is the water levels in the two tanks. If the boiler header tank has the higher level and the cylinder coil leaks then water from the header will find its way up the cold feed and into the cold tank. It might NOT be able to flow over the vent so open that cold feed valve again and see whether your header tank keeps on filling up. If it does then it's going somewhere.

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