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Expansion pipe dripping

Posted by David Thurlow, on
I have a sealed hot water and heating system. The expansion pipe from the hot water cylinder is dripping into my cold water tank in the loft. I have replaced the hot water cylinder. If I turn off the mains water supply the problem continues. The water supply both hot and cold to the showers and taps upstairs is from the cold water tank in the loft and not the mains so I guess the pressure is the same for both hot and cold. Any ideas how I can solve the problem, my plumber has none.
Massimo Liguori

Massimo Liguori

Are you sure you have a sealed hot water system? From what you are suggesting, i.e. that your hot water cylinder expansion pipe is dripping into your cold water tank, you are describing an open-vented hot water system, where the vent pipe is discharging into the cold water tank. If you have a sealed or unvented hot water cylinder, you would not have a cold water tank in the loft, since the cold supply to the cylinder would be at mains pressure (reduced to an appropriate pressure via a pressure reducing valve). Thus, if you do have an open-vented hot water cylinder, water would travel up the vent pipe when the water being heated in the hot water cylinder expands. With a correctly installed and set system, it is unlikely that the volume of expanded water would expand into the cold water tank. Is the cylinder thermostat working? If not, it could be that the cylinder water is boiling which would cause it to expand into the loft.

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