Central heating expansion/feed tank red hot.

Postby Robosn » Mon Nov 03, 2008 11:16 am

I have installed central heating and understand the system. My daughter has just moved into a new house and tells me there is a loud banging when the hot water/heating starts up in the morning.

Sounded just like air in the system but it seems they have bled it regulalry so I asked her husband to go into the loft and check the c/h header/feed tank and to look for any bleed screws which are sometimes fitted in the highest position.

While there, he found the headerfeed tank to be red hot and couldn't be touched which seems to me to indicate the c/h pump is pumping the c/h water back up into the header tank.

Has anyone had this problem and got any ideas before I go there?
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Simply Build It

Postby TheDoctor4 » Mon Nov 03, 2008 4:11 pm


Have you had a look at the DIY projects area: http://www.diydoctor.org.uk/projects.htm There are several projects relating to Central Heating that may provide you with some assistance with this issue.

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Postby chris_on_tour2002 » Mon Nov 03, 2008 7:06 pm


People have died from such faults - one young girl died in her bed just this year in fact. It was big news in the national press. The tank will eventually buckle and fail under the heat of the water spewing boiling water down through the ceiling and into the room below. You are best off staying out of the loft and the room directly below the tank until it has cooled.

The real tragedy is that it is usually caused but such simple fault, one that can easily be fixed.

Normally this happens when the cylinder thermostat develops a problem and fails to tell the boiler that the water is hot enough and that the demand has fulfilled and the boiler can shut down or divert to heating only. this causes the water in the cylinder to get hotter and hotter until it expands up into the cold water storage tank. this draws more water back into the cylinder to be heated, and expands back up into the tank until all the water in the tank is boiling.

if this is happening in your F&E then it sounds like the boiler is just running and running. this could also be due to a faulty thermostat. you need to get this looked at before you start using your system again.

if not sure what you are doing then call in a qualified heating engineer.

It cannot be stressed enough how important it is to refrain from using the sytem until it is fixed. The consequences can be disastrous.
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Postby plumbbob » Mon Nov 03, 2008 10:55 pm

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Postby Robosn » Sat Nov 08, 2008 1:24 pm


Thank you very much for your words of wisdom. I am visiting her tomorrow and will know much more then. Fortunately, and unusually, the expansion/feeder tank is apparently galvanised steel so not quite as dangerous as plastic but nevertheless, it needs to be sorted urgently.
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Postby Robosn » Mon Nov 10, 2008 3:06 pm

I thought it may be helpful to others if I explain what I found when I visited her home concerning the expansion/feeder tank getting very hot.

The vent pipe had been left touching the water in the expansion tank and a separate circulation was taking place. The tank water had become boiling hot, had filled up and was overflowing.

By draining surplus water from the tank and removing a section from the vent pipe so it could not touch the water, it appears to have solved the problem. Obvioulsy I will be keeping an eye on it for a while.
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