Hot water overflow from cold tank

DVardysShadow

I too suspect the coil. As the CH header tank is higher than the DHW header, a leak will fill the DHW header naturally. A leaky ball valve will not result in lukewarm water in the tank, not this time of year. If the CH is venting into the wrong tank or the immersion is venting into the right tank, you would expect to find the vent pipe warm and evidence of water flow in progress.

AdrianW2

The British Gas engineer has just been out and he suspects the coil too, so it's new HW tank time.

Apparently the sloshing sounds from the tank are a bit of a give away.

1984ReturnsForReal_2

AdrianW2 wrote: »

The British Gas engineer has just been out and he suspects the coil too, so it's new HW tank time.

Apparently the sloshing sounds from the tank are a bit of a give away.

Have you had discolouration of your cold/hot water?

a&akay

AdrianW2 wrote: »

We've been having some trouble with our water recently. The cold water tank in the loft has been overflowing. When I look in the loft the tank is full and steaming, and the water lukewarm.

The float valve is about 6 months old and appears to be working fine.

So I suspect something in the hot water system is dumping hot water into the cold tank through the vent pipe.

There are lots of similar posts on the web, but I don't really understand the answers so any suggestings of what to check gratefully received.

As an aside, last week we changed one of the taps and I turned the water off to do so and forgot to turn it back on before the heating kicked in. I'm not sure if that's relevant but the cooincidence is suspicious.

Should be fairly easy to prove it's the coil. If so, the driver that's pushing the water from the small feed and expansion tank into the hot water tank is the difference in water level between the level in the small CH feed tank and the level of the overflow on the bigger hot water cold feed tank. It's the outflow from this that you are apparently seeing. Stop the flow into the small CH feed tank by holding up the ball valve (or valve on the cold feed to it if there is one) and empty your hot water tank a bit by opening a hot tap nearby. The amount you need to waste is the few gallons in the small CH feed tank plus a bit in the intervening pipework. If it's the coil, then the overflow will quickly stop because the top up will be via the leak in the coil. (The leak in the coil would also be pumping some hot water from the central heating side, when the CH's on, straight into the hot water system, ie not heating it separately only via the coil).

AdrianW2

Well I was just about to post a message singing the praises of British Gas Homecare.

We've had a new cylinder, pump and 3-way valve. All installed efficiently by friendly engineers. Their call centre being the only disappointment.

Unfortunately there's still an overflow! This time it's the central heating feed and expansion tank. When the boiler central heating timer turns off there's a lot of noise and activity for about 30 secs. I got into the loft in time to catch water in the F&E overflow pipe, with puddles underneath it, but the tank levels perfectly normal.

Looks like another weekend waiting in.

ormus

its possibly just the vent pipe is not long enough.
when the pump stops, any water still in the boiler will boil for a minute or so.
thats the water that is venting up into the tank.

you might try turning the boiler heat down a peg, and see if that helps?

Moss5

Could be air-bubble 'bounce'
Try bleeding all your radiators (with the pump off) and any other bleed points provided.
If that fails, try turning the pump speed-selector to a slower setting.

AdrianW2

Nothing seems to be coming out of the vent pipe - I've watched, the pipe is cold and there's an intact cobweb.

One of the upstairs radiators is cold, so it I'll try bleeding it, but the BG people bled the radiators two days ago.

I suppose it could be just that the float is set too high.