Hot water in the cold tank and system overflowing

17 Feb 2007
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United Kingdom
Hi, the domestic hot water in my flat is heated and stored in a foam covered tank that is about 6 feet tall. ? its age. There is a smaller section at the top, where cold water feeds in, and a larger section at the bottom where the hot water sits. There are two pipes that connect the two tanks, one from the bottom of the cold tank to the hot, and one from the hot that opens in the top tank above the water level. These are hidden beneath the foam but you can see their outline. Just recently, the top tank began to overflow and I fixed the ballvalve and the overflow pipe that was sludged up. What is happening now is that hot water is venting into the top, cold water tank. This eventually heats all the water in this tank and this is making the airing cupboard rather like a sauna. I don't think this should happen... I've not noticed it before, but I feel that this was contributing to making it overflow ? There are two immersion heater elements in the bottom tank, one near the bottom, an economy 7 one, and one near the top that is wired into the normal circuit. Can you please advise on a plan of action. Thanks
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Could be a thermostat in one of the immersion heaters failing to cut out at temperature. If the top one is the "boost" and can be switched on/off then it must be the E7.
Thanks for your reply solo. I tested the elements and it was the top 'booster' one that had gone. Got it sorted now. cheers

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