feed tank overflowing

The feed tank for my hot water/central heating keeps overflowing even though I've replaced the ball valve and adjusted it so the water level is well below the overflow pipe.My system is feed from the hot water copper tank this has a valve which looks like a copper mushroom,I gather there is a pocket of air that get trapped under the mushroom and this keeps the central heating water and hot water from mixing and if the pressure drops in the central heating the hot water tank tops it up.The feed tank overflows only when the central heating is on so I was wondering if back pressure could be forcing water back into the feed tank.My bolier becomes noisey when this happens but after I bleed the boiler and rads its ok for a couple of weeks but always returns.I originally thought the problem was caused by a restriction through the boiler so I removed the heat exchanger and cleaned it out as it was partially blocked.The only other thing I can think of that might be causing the problem is 2 valves which I think are used to balance out the system so water is not forced back into the copper tank, I did have a go at adjusting these but they made the hot water brown so I put them back.Sorry for the long post but I'm hope someone out there has experience of this oddball system.

Cor did the installer come from durassic park. have u extended the system at all lately.If not then its really time to drag that out of the dark ages & fit a seperate f/e cistern. sorry

Bryan, this sounds like a Primatic cylinder. If so, your system is really rather old, and the prospect of trying to diagnose your problem via the keyboard is not going to be palatable for any heating engineer on the forum.

As per bab's suggestion, you'd be best off engaging a professional to take out the old cylinder, and replace it with a lovely new indirect jobbie, and add an F&E cistern if you don't have one. It might not be cheap, but you wouldn't regret it, assuming you find someone competent...

I thought that would make you laugh. British gas installed the central heating 15 years ago and I added a new radiator 12 years ago but I have only had the problem for the last 3 years. In that time I've removed the rads a couple of times and reversed flushed them as well as flushing the whole system a couple of times with flushing agent and when I refill I use inhibitor. The reason they told me they didn't fit a separate feed tank because where the boiler is situated it it would have been difficult to do and there would be a hefty additional cost.

Hi softus. If im right what Bryan has (which i hav only ever seen once before but never forgot)is a mini type of a primatic cylinder in sides, connected to an indirect cylinder. he adds inhibiter. Still should'nt. it only reduces the need for the f&e but is as much work to fit. the guy who came up the idea is probably dead & should be.

Hi bab - I'm impressed by the things you've seen, but hope that I never have to

Saw it in an airing cupboard in a flat in Blackpool. enough said. (FLEA PIT)

So my guess that the hot water and the central heating water are only kept apart by a pocket of air was correct then. Is that why you say I shouldn't use corrosion/sludge inhibitor because the chance of it getting into the hot water is too great.Surely this type of system shouldn't have passed any regulations even if it was 15 years ago.We have suffered brown water on several occassions but its usaully after I have done work on the c/h and all I've done in the past is run off the hot water until it runs clear. I think I will contact British gas to see what they say.

bab said:

Cor did the installer come from durassic park. have u extended the system at all lately.If not then its really time to drag that out of the dark ages & fit a seperate f/e cistern. sorry

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Steady , I`m the Prehistoric Plumber here Odd balls........copper mushrooms.....Crazy, Man BG will say HaHaHa.all the way to the bank I`ve seen one of those mini tanks .and better still.......I saw a Servowarm system with a plastic vase screwed to a wall that you kept topped up..as the feed/expansion that was back in the 70`s, Man

Get that plumber round that caps off overflow and safety pipes.

bryan walker said:

...I think I will contact British gas to see what they say.

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S'funny old world - hearing what British Gas will say to me is the very reason I avoid contacting them!