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Stuart 08-03-2005 06:16 AM

Header Tank Overfilling (still)
The large header tank in my loft (hot water system) keeps overfilling and overflowing through the overflow pipe. I have changed the ball valve washer - no change. I have replaced the ball valve (using a non- syphoning replacement) - no change. I don't think the ball valve can be the problem but I don't understand where the extra water is coming from! The problem is slow (overnight) and does not seem to be a problem when we are using lots of hot water.

MgMopar 08-03-2005 07:24 AM


Lets first start by saying I am not familiar with your system. I am only visioning it from your description.

With that said, I can only think of two places your mystery water would be coming from. First expansion. How close to the overflow is the water when it shuts off. Could the water be getting enough warmer when not in use to expand to the overflow? Second possibly I can think of Do you have any single valve faucets or shower valves in the home. The kind were both hot and cold are controlled by a single knob? Maybe pressurized cold water is seeping past seals into your hot water system (kind of like an internal faucet drip) If this is the case it would most likely be a minimal loss but could overfill the tank after long periods of time.

dirkgently 08-07-2005 12:44 PM

If you have a vented central heating system (small feed & expansion cistern in roof space) and the F&E cistern is above your main cistern, there may be a hole in the annulus of your hot water cylinder, in which case you will need a replacement cylinder.

Bob Ellis 08-16-2005 02:53 AM

Header Tank Overfill
I too had this problem. I eventually tracked it down to the heating system where there is a surge when the hot water boiler goes on first thing in the evening and then first thing in the morning. I went through the normal DIY process of changing valves etc but to no avail. This happened 13 years ago and had to replace the hot water tank in the airing cupboard which cured it. Unfortunately this is happening again and must shell out once more before the colder weather sets in with the possibility of the overflow pipes freezing up. :(

Stuart 08-16-2005 10:23 AM

Solved - I think.
I saw the advice posted and tried isolating mixer taps to locate the problem. It came down to a basin mixer tap (single valve controlling hot and cold water). When this is isolated the problem seems to stop. I removed it and then found I could have dis-assembled it in-situ (never mind!). The plastic / ceramic internals had some damage which seems likely to have allowed cold pressurised water to leak over to the hot water side even when the tap was closed.

As the tap is only 2 years old I sought replacement internals from B&Q (in the UK) who supplied the original. They did not keep them and refused to tell me who was the manufacturer so that I could seek parts elsewhere. However, after trying again over the phone, B&Q (or their supplier) have promised to send me the parts free-of-charge in the next few days.

Problem solved - hopefully. Thank you.

Cliffox 10-25-2006 03:56 AM

Headertank overflowing
I read the notes here as I have a similar problem. Having changed the ball valve twice I realised that this was not the problem and have watched water flowing back into the tank via the expansion pipe. I also saw a surge in this flow when the mains water was turned on, after replacing the ball-cock... Now I need to check which tap might be causing the feedback... as I only have one mixer tap that is connected to mains pressure I thought that this might be the culprit BUT after isolating this one for a few hours the drips persist...
I will isolate the bathroom taps now (that are fed from the cold water header tank) and see whether they solve the problem... after that I guess I will have to investigate the possibility that it is either a leak via the hot water cylinder or via the actual boiler...
ANY comments welcome!

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