Overflow in main water tank

22 Sep 2009
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United Kingdom

I live in the UK (if that matters!) and have a problem with the water tank in the loft: it keeps overflowing.

I have fitted 4 new brass equilibrium ball valves in the past year. For a month or so they seem to work okay (shutting off the water as the water/ball float rises), but after that the water just doesn't shut off completely. It trickles all the time and eventually overflows (usually overflowing each morning via the outlet at the edge of the roof - you have to turn on a tap in the loo to drain some water out).

If I pull the arm of the valve up hard, the water will just about shut off but if the ball float is used by itself, it just doesn't create enough force to close the valve (the ball just gets submerged by the water).

I have looked at the valves I have replaced and they all look okay - there is no visible damage. The washers look okay.

There is a stop cock in the kitchen downstairs by which I can control the speed of the water going up to the tank in the loft. I only have this open about an eighth of a turn, but still the flow of the water into the tank in the loft is very hard. There is also a "tap" in the loft just by where the pipes enter the tank, but however hard I turn this, it makes no difference to the flow of water into the tank. I can only stop the flow of water if I close the stop cock in the kitchen.

I can't find the mains stop cock outside the house .... there's no little pit anywhere in the road (the house is very old - I don't know if a mains stop cock even exists for it).

I think the ball float on the arm is about 4 or 5 inches round.

If this was bigger, I guess it would have more force with which to shut off the valve as the water rises.

Is it possible to get an arm which takes 2 ball floats ... in order to double the closing force on the valve? I have looked online, but not been able to find anything.

With thanks in advance.

Mac :D
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whats the tank made of :?:

Thanks for the reply. Some kind of plastic. All the fittings to it look like brass.

The tank itself isn't leaking .... it is just that the valve isn't shutting off. The force created by the rising ball valve doesn't seem enough to make the valve close....

are you sure the tank is not flexing enough to allow the overflow

the ballvalve should have a plate on to stop this but i can't remember the right name for them

looks like a strip of metal with a hole in the top for the valve

i'm sure somebody will shortly post the name ;)
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Ah, I see. But I am sure the tank isn't flexing. It is very rigid. It is about 5 years old and very sturdy.

When I have bought new equilibrium valves, I have replaced the entire units ... so I don't *think* anything is missing. But I'm just an inexperienced and not very competent DIYer, so I might be wrong.

We've had the problem for the last 2 to 2.5 years. Originally, I had plumbers fit new ball valves for me (3 plumbers fitted 4 ball valves). The last plumber showed me what to buy and what to change if the thing started playing up again. In the last year, I have fitted 4 new valves myself - so in the last 2.5 years, we've gone through 8 units. I was hoping I could find a solution that would work in the long term.

Thanks for the 2 replies above.

The thing I keep replacing LOOKS like this (might not be exactly the same):


The water level looks like it should stop about 4 or 5 inches below the level of the overflow ... but it doesn't stop filling up ... as the ball rises, the flow rate does slow down, but it doesn't stop. The water continues to trickle all the time and the water rises over the float.

I have bent the arm down so that the float sits lower in the water and in theory this should shut the water off .... but it doesn't .... it just trickles all the time.

If we use the taps during the day, it doesn't overflow as the water level drops. But at night, the water level keeps rising and in the morning we have a steady trickle of water coming out of the overflow pipe at roof level.

I am not sure what "backing up" means!

It is the main water storage tank that is overflowing, not the little header tank next to it.

I saw floats on this site:

(go to the bottom of the page) and was thinking of buying some different sizes and trying them. Don't know what the 5/16 7/16/ 9/16 etc refers to.

Maybe I should just get a plumber back again ;-(

Do you have very high pressure.

The 5/16 refers to the thread on a standard valve arm.

I think we do. I don't know any way to measure the pressure, but as a layman's guess from comparing the other places I have lived in, I would say we do. This is the strongest water flow of any house I've ever been in. We're out in the country. Don't know if the water comes from a bore or what. We're the second house in the village, so I guess there must be a fair amount of flow at our end.

There's a stop cock in the kitchen downstairs which can shut off the water going up into the tank. We only have this stop cock open about an eighth of a single turn ... it really is barely open and yet we have got lots of water flowing into the tank. If I push the ball float down by hand (to open the valve fully) the water gushes out very hard.

Thanks for the 5/16 advice. I guess that's what I could try ... a larger ball with a 5/16 thread on it as I am sure it must be a standard fitting.

torbeck might work View media item 674
thats a bottom entry but you get side entry as well

Thanks, again.

I thought brass was meant to be better/stronger/longer lasting than plastic, but I'm happy to give anything a go. Appreciate the advice. Will see what I can get from the local plumb centre.


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