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Mystery hot tank overflow - any ideas/suggestions?

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Stevel

from United Kingdom

Joined: 10 Aug 2004
Posts: 39
Location: United Kingdom

PostPosted: Mon Apr 02, 2012 2:35 pm Reply with quote

My Setup:
Electric boiler, heating HW / CH - I have a gravity-fed hot tank and header tank in loft.

My Problem:
When turning on the HW for a downstairs shower, after between 12-24 hours, the header overflow starts trickling with water. The ball valve is operating fine, but the expansion pipe for the cylinder leads to the header tank.

I have tried really hard, but can't work out why the overflow is, er, overflowing. Pressure? Air intake? Leak anywhere?

The pressure is on for me to tile the shower, so would really appreciate any help in solving this one!
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picasso

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PostPosted: Mon Apr 02, 2012 3:17 pm Reply with quote

cold mains water and gravity hot water feeding the shower ?
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TonyW2

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PostPosted: Mon Apr 02, 2012 4:01 pm Reply with quote

picasso wrote:
cold mains water and gravity hot water feeding the shower ?

But if that pressure difference into the shower mixer was the source of the extra supply into the feed tank, the shower would always deliver only cold.

OP says it happens after 12-24 hours. Are you sure that the ball valve is shutting off? It may be that at most times, water use is sufficient to use the excess supply and that it builds up when there has been no use for a long period.
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leakydave

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PostPosted: Mon Apr 02, 2012 4:02 pm Reply with quote

Cylinder coil leaking water from one cistern to another?
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Space cat

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PostPosted: Mon Apr 02, 2012 4:16 pm Reply with quote

TonyW2 wrote:
Are you sure that the ball valve is shutting off? It may be that at most times, water use is sufficient to use the excess supply and that it builds up when there has been no use for a long period.


That would be my first guess. Test it. Next time the header tank is overflowing, don't use the shower. Don't use any hot water at all; just scoop a jugful out then wait to see if it fills up again. icon_idea.gif icon_idea.gif icon_idea.gif The best time to do this would be last thing at night.
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picasso

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PostPosted: Mon Apr 02, 2012 4:21 pm Reply with quote

TonyW2 wrote:

But if that pressure difference into the shower mixer was the source of the extra supply into the feed tank, the shower would always deliver only cold.


If you throttle the cold down enough you can roughly balance the hot and cold, its bad idea to install like this but its seems to be a favourite short cut for diyers,

the reason I asked about the hot/cold supplies is the check valve in the shower could be passing letting cold flow back up the hot supply to the tank, or any where the mains water and hot meet ie kitchen mixer, washing machine installed with y connector ect.
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Stevel (2 Apr 2012)
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Stevel

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Location: United Kingdom

PostPosted: Mon Apr 02, 2012 4:25 pm Reply with quote

I had two lever-style isolation valves for the hot and cold put into the ceiling of the DS shower room. The overflowing only occurs when the hot valve is open, and can be stopped when it is closed (not instantly, but after a few minutes).

The 12-24 hours reference is to when this valve is opened. We have had hot water going to DS and the US Bathroom for over a year with no problems.

I should also add that the valves are the end-of run.

This probably makes this even more odd!

Thanks for the ideas already - I will turn hot valve on and 'jug out' the header tank to see if it is the ball valve. Is is worth somehow collecting water from the expansion pipe?
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foxhole

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PostPosted: Mon Apr 02, 2012 4:38 pm Reply with quote

Is the overflow pipe above header tank securely fixed, mine came loose and dropped causing siphoning and overflow of tank whenever it was heating.
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Stevel

from United Kingdom

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PostPosted: Mon Apr 02, 2012 4:42 pm Reply with quote

Quote:
If you throttle the cold down enough you can roughly balance the hot and cold, its bad idea to install like this but its seems to be a favourite short cut for diyers,

the reason I asked about the hot/cold supplies is the check valve in the shower could be passing letting cold flow back up the hot supply to the tank, or any where the mains water and hot meet ie kitchen mixer, washing machine installed with y connector ect.



This actually makes a lot of sense. The shower certainly is a 'mixer' type, with two handles, one for flow, and the other for temperature. Is it worth adjusting the temperature on the shower so it is v cold, as in, shutting off the hot?[/quote]
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Space cat

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PostPosted: Mon Apr 02, 2012 5:00 pm Reply with quote

Stevel wrote:
The overflowing only occurs when the hot valve is open, and can be stopped when it is closed (not instantly, but after a few minutes).


Well that changes things a bit. You can forget about the ball valve for now. Water is backing up the hot pipe from the shower - very slowly since it takes at least 12 hours for it to reach the overflow. The fact that you can stop the dribbling by shutting the hot valve pretty much clinches the diagnosis. The question now is this: Where is the excess water coming from? icon_confused.gif icon_confused.gif icon_confused.gif
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The following user says thank you to Space cat for this useful post:
Stevel (2 Apr 2012)
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Stevel

from United Kingdom

Joined: 10 Aug 2004
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Location: United Kingdom

PostPosted: Mon Apr 02, 2012 5:09 pm Reply with quote

picasso wrote:
TonyW2 wrote:

But if that pressure difference into the shower mixer was the source of the extra supply into the feed tank, the shower would always deliver only cold.


If you throttle the cold down enough you can roughly balance the hot and cold, its bad idea to install like this but its seems to be a favourite short cut for diyers,

the reason I asked about the hot/cold supplies is the check valve in the shower could be passing letting cold flow back up the hot supply to the tank, or any where the mains water and hot meet ie kitchen mixer, washing machine installed with y connector ect.


HUGE THANKS to PICASSO - your hunch was absolutely right. This is what we did to test and solve the problem:

Put the HW to advance, filling up the cylinder with hot.
Opened the hot iso valve.
Turned shower on, and turned it to hottest setting.
Checked hand temperature of hot by valve - hot to touch.
Cup of tea.
Sudden influx of water on kitchen roof from overflow pipe!
touch hot valve - now very cold!
Turned off Hot at valve
flushed toilets to give Header Tank some space.

Will now search out new shower mixer and 'file' old one. Never liked it anyway!

Thanks again to all those who contributed a solution!
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TonyW2

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PostPosted: Mon Apr 02, 2012 5:29 pm Reply with quote

12 to 24 hours to drink tea???? icon_wink.gif icon_smile.gif icon_smile.gif
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Stevel

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PostPosted: Mon Apr 02, 2012 6:27 pm Reply with quote

I've done a bit of research, and it would seem I could add a check valve to the hot pipe. Is this hiding the problem, or would this be a good move?
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duffin

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PostPosted: Mon Apr 02, 2012 6:49 pm Reply with quote

don't bother with a check valve- although this would work. change the mixer and make sure it's suitable for gravity systems.
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linkyplumb

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PostPosted: Mon Apr 02, 2012 7:43 pm Reply with quote

High pressure area?

Had this once with a combination cylinder. At off peak demand pressure got to over 12 bar and caused ball valve leak, thus overflowing.
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