Help! Hot water tank overflowing

10 Apr 2007
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United Kingdom
We have a small, rectangular hot water tank in the loft which has started to overflow via the overflow pipe outside. I've had a look in the tank and can see a ballcock and that hot water is being fed continually into the tank (this could be normal considering the heating and hot water are on at this time?).

I assume that when the tank is full somehow the hot water feed should be turned off and this is what is not happening. Any ideas what I should be checking to stop the overflow?

We have a gas boiler, hot water cylinder in the airing cupboard, and two tanks - one large cold tank, and this small hot tank - in the loft if that helps at all.

Many thanks in advance!
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that tank you say is hot should be cold.
sounds like your system is pumping over.
is the hot water comming out the copper pipe that is hanging over the top of the tank ?
>> that tank you say is hot should be cold.

Eek! It's very hot - too hot to touch the ballcock.

Out of interest, what is the purpose of that tank then?

>> sounds like your system is pumping over.

What is 'pumping over'?

>> is the hot water comming out the copper pipe that is hanging over the top of the tank ?

Yes it is.

Thanks for helping.
I had a look in this thread: // So it seems that my tank is an expansion tank and it may be possible that the boiler stat has gone? Is this a good guess?

Another symptom I noticed recently is that the central heating doesn't seem to turn off as quickly as it should when the house warms up. I put that down to a dodgy thermostat. Maybe it's related to this tank problem?
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:eek: :eek: :eek:

Luckily it seems my legendary fiscal tightness didn't stop me from signing up to British Gas Homecare 200 which seems to cover this. An engineer is coming tomorrow afternoon. Until then... cold showers. :evil:

Thanks for the assistance. Much appreciated!
BG have been and the bloke said that there is a blockage in the pipework by the air separator which he detected using a magnet. Apparently the air separator slows the water flow down and deposited sludge and metal deposit can then bung the pipework up. The fix is to cut out the pipework and seperator and replace it with a H section instead as apparently the air separator doesn't do much anyway. He couldn't do that today so turned down the pump, checked the expansion tank to check it wasn't deforming, and is going to come back next week.

Unfortunately homecare 200 doesn't cover this so it'll cost £39. Not too bad in the end. Phew.
for an extra £100 or so you could get a Magnaclean which will attract and trap all the circulating sediment and prevent future blockages.
Thanks for that tip, JohnD. I've read all the information on their site and had a look at the Boiler Buddy too. Very interesting products! I want to get a new boiler within the next year or so and it seems that it wouldn't hurt at all to get one of these now. I'm wondering if it'll do away with the need for a powerflush when the new boiler is installed. Wonder also if I could get the BG man to install one while he's fixing the blockage.
After fixing a Magnaclean, I added X400 and it loosened an amazing amount of black sludge that had built up inside the system, and it then got trapped on the magnet. You can do the chemical clean and flush yourself. it's easy DIY work.

I expect that when you buy a new boiler, the installer will insist on a powerflush as a condition of the guarantee, but I see no harm in getting the system as clean as you can before that time comes. it will prevent future blockages building up and will generally improve efficiency.

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