Mystery hot tank overflow - any ideas/suggestions?

[Stevel]

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!

 

[picasso]

cold mains water and gravity hot water feeding the shower ?

 

[TonyW2]

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.

 

[leakydave]

Cylinder coil leaking water from one cistern to another?

 

[Space cat]

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. The best time to do this would be last thing at night.

 

[picasso]

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.

 

[Stevel]

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?

 

[foxhole]

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

 

[Stevel]

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]

 

[Space cat]

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?

 

[Stevel]

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!

 

[TonyW2]

12 to 24 hours to drink tea????

 

[Stevel]

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?

 

[duffin]

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

 

[linkyplumb]

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.