Combination cylinder

10 Oct 2006
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United Kingdom
I have been asked about a problem with a combination cylinder - the hot water is coming up and into the cold water storage tank of the cylinder. This is after fitting a mixer tap in the kitchen. When either the cold or hot water to the mixer tap is isolated the problem does not occur. Am I correct in assuming that due to the high pressure from the mains cold supply is fed back to the hot part of the cylinder and pushing this water back up into the cold tank. Ball cock in the cold tank is working correctly. Any thoughts?
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Yes you are correct. Fit check valves (non return valves) to both the pipes.
A check valve has been put on the hot to the mixer tap and has solved the problem, the hot water now takes about 10 secs to come out of the mixer when tap opened - why? What is the purpose of the nut on the check valve?
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Yes it's great fun when you are between first and second fix on a job and you turn cold water on so customer can use the toilet, only to be called out in the night by them having used a mono tap and the cold water getting piped out of an open end elsewhere. Don't tell me it only happens to me, I know.

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