cold water storage tank overflow

12 Jun 2008
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United Kingdom
Returned recently from a week on holiday and decking under the CWST overflow was quite wet.

After normal water usage all was ok until a couple of times a little water evident first thing in the morning.

I've searched the forums and I am going to replace the ball valve.

However, looking in the tank it does not seem like the water level has ever reached the top of the upstand overflow pipe and the valve seems to be shutting off correctly.

We have had a kitchen mixer tap for some time and I dont think there are any NR valves fitted so perhaps this is the culprit - but why now? And would there not be evidence of high water level in the tank?

The other thing mentioned briefly in another thread was the fitting at the bottom of the upstand could be leaking. This one makes sense to me but would it not leak outside all the time?

As I said, I'll change the ball valve but I'm not confident it will solve the problem.

Any advice or suggestions most appreciated
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If the overflow pipe is wet, then the tank level must be rising unless the upstand pipe has a slight crack to its upper part, allowing water in there somehow......
Sometimes the overflow is shared with the heating flow and expansion tank - is this possible?
John :)
Hi John
Thanks for your quick reply.

The CH expansion tank was removed when new boiler fitted a couple of years ago.

I'll check for cracks at top of stand pipe.
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Changing the ball valve is so easy and cheap to do, you should do it anyway.

I reckon it will solve the problem. It's common for them to drip slightly no water is taken from the tank for a long time, such as when you're on holiday, then behave themseleves (for a while) when the tank's in frequent use again.
See what you mean, John. Maybe the fault wasn't there for long enough to leave a tide mark? :confused: ;)
Thanks for all your replies.

The other puzzling thing about the water level is that it is 2-3" below the top of the overflow pipe. So unless it's cracked as John suggested I would expect it to be very near the top after I see the water outside.

Slight aside - I was looking on the net at various items and came across byelaws 30 & 60. Since I live in Scotland do I have to consider byelaw 60 for the new ball valve?

Are any of your bath taps mixer taps. I had a leaky mixer tap with no NR valves fitted to the pipe and had a back syphoning into the storage tank causing the tank to over fill. With the levels reducing in the tank once the cold water tap was opened it didn't give it enough chance to leave a high water mark on the tank.

Check all mixer taps in your house to see if any are leaking. The slightest leak could cause back syphoning and would be remedied by replacing the mixer tap.
The bath tap and bathroom basin tap are mixer taps but fed from cold water storage tank - not mains cold water.

Are any of them leaking?

What's your hot water pressure like? If the cold pressure is greater than the hot pressure, you still might be able to have back syphoning.
Are any of them leaking?

What's your hot water pressure like? If the cold pressure is greater than the hot pressure, you still might be able to have back syphoning.

By Leaking do you mean dripping? or do you mean leaking underneath?
No sign of either.

I filled the basin to the overflow with hot and cold individually.

Hot 60 seconds, cold 70 seconds, so hot pressure is slightly higher.

Hot flow rate is higher, but not necessarily the pressure ;)[/quote]

So how can a layman (me) check the pressure, Chris?

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