Header Tank Overflowing - Not the Ball Valve

Postby sbarrick » Fri Jul 09, 2010 5:00 pm

Hi All

This is my first post on the forum, and know little about plumbing. But here is my problem.

My header tanks keeps overflowing. I have replaced the ball valve and checked this several times for leaks to which there is none. So I can confirm that it is not the Ball valve. The tank in the loft continues to fill up over a number of days and overflows via the overflow pipe outside. We have not had our central heating on or the emersion heater and still it is filling up. HOW????

I tested this today, no heating or emersion heater and did not use the hot water for several hours and the tank water depth rose by about an inch.

Our system is an indirect vented system with tank in loft. The Tank is a Showmax Supercal Cylinder.

Can someone please help with advice.
Posts: 1
Joined: Fri Jul 09, 2010 4:02 pm


Simply Build It

Postby tebsin » Mon Jul 12, 2010 7:07 pm

This is also my first post and I have exactly the same problem, I have also replaced the ball valve.

I can stop this overflow by turning off the feed to the copper cylinder from the smaller central heating header tank which is slightly higher in the loft by 1 ft.

I think the heat exchanger pipe inside my indirect cylinder which is fed from the small header tank is leaking, and the water levels are trying to balance out by flowing into the rest of the indirect cylinder and up into the storage tank, thereby causing the water to rise and run out through the overflow??

I took the temperature of the water in the cold water tank and it is very warm, a lot warmer than the smaller central heating header tank, the boiler is off but my immersion is on.


Does anyone have any ideas apart from a new indirect copper cylinder which is 40 years old ???
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Joined: Mon Jul 12, 2010 6:50 pm

Postby wickstead » Tue Jul 13, 2010 4:40 pm

My first time too.
I found this problem on a customers house and sourced the problem back to a shower valve.
some shower valves have too have a balanced inlet, some don't.
The problem with some installations is that the plumber has connected up with mains cold too the valve and gravity fed hot, so, the cold pushes the hot back up to the tank, the tank then overflows back up to the cold storage tank via the expansion pipe, thus causing the cold water storage tank to become warm.
Change the valve for an unbalanced type or add a pressure reducing valve to the cold inlet to the said valve.
hope this helps.
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Joined: Tue Jul 13, 2010 4:25 pm

Postby tebsin » Thu Jul 15, 2010 6:18 pm

An update.
I noticed the central heating header tank was filling all the time at the same rate as water was coming out of the overflow in the cold water storage tank so I bit the bullet and took out the hot water cylinder, this was 42 years old and I cut it open with an angle grinder, the coil had holes in it letting the water through and the tank was full of black scale. I presume from the boiler.
Unfortunately as it was so old the connections were at different centres so I had to alter all the pipework, which was £87 for fittings and pipe and £190 for the new indirect tank and immersion. It took all day.
Hope this helps others

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Joined: Mon Jul 12, 2010 6:50 pm

Postby htg engineer » Thu Jul 15, 2010 8:43 pm

Does it happen when mixer taps or mixer shower or bath tap/shower adapter ?

Quite common as mains cold water pressure is greater than the stored hot water - if you open cold fully - it can backfill the tank and overflow.


Didn't see wickstead's post - only way really - if boiler turned off and ballvalve ok/not filling tank.
htg engineer
Posts: 3193
Joined: Tue May 22, 2007 5:22 pm

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