Lovely Sunday DIY project of replacing my water tank ball cock, and have fallen at the first hurdle….. I’ve turned off my mains stopcock under the sink but this seems to have done bugger all to the flow. Any ideas as to what I’m being a numpty about?!

Stop cock was feeding a header tank on your attic which is now filling your cistern even though the header tanks not topping up now due to the stop cock being off ?

Is it a stop cock or a Gate valve (this has a red circular metal turn handle) if so the valve is spinning inside

when you say “flow”…

do you mean that

1) the cold water continues to flow out of the hot or cold taps in the kitchen?
2) in the bathroom?
3) at the inlet to the water tank cistern?

No it’s definitely a stopcock, , to be clear it’s the pressure into feeding the mains tank in the attic. After turning “off” the stopcock how much do you think will be in the system to drain before I’d see no flow into the attic tank?

Stoner – answer number 3 🙂

You could freeze the pipe and put in a stop cock nearer the tank.

you shouldnt see any flow into the attic tank when you shut off the rising main at the stopcock.

Id go and look for another stopcock if I were you…(or check the one you’ve twiddled is not knackered)

Have had a hunt in the airing cupboard for another stopcock but nothing obvious to be seen. Thanks for the input and thoughts!

stop cock is usually located under or near g/f sink as the kettle gets fresh water first not from a tank in airing cupboard.

How old is your house??
If it’s under 20years then you might just have a ball valve by the tank!
The feed for the tank will be from the mains so as mentioned above the shut off valve should be under the kitchen sink

When you turn off the valve under the sink does the kitchen cold stop running or just your outside tap.
Main valve can be under stairs, near the front or even in you neighbours kitchen (yes I have seen that, and sorted it!).
If none of these work you may need to switch off the main outside in your drive/front yard/street or neighbours yard (yes I’ve seen it too but not worth changing once you know where it is.
Are you changing the ball valve in loft tank or WC.
If it’s WC you can Bing the main storage tank cold supply.

Good luck.

The main stopcok should be a proper brass tap right where the blue pipe emerges from the floor. If you’ve turned off a gate valve with a red handle, it’s probably Chinese and won’t shut fully.

How many turns does it take to turn the stopcock from fully on to what appears to be ‘off’? If ours has not been turned for a while, it needs an adjustable spanner to get it to turn off properly. I assume the hard water is furring it up somehow.

For diagnostic purposes, an almost closed valve results in the same pressure, at low flow. Only in high flow does the reduction become visible. So unwind the valve fully, and see what flow you get from a bath tap. Then close it as far as possible, and see what the difference is. If there’s no difference in flow, the valve is on a different pipe!