Turned off water - still flows?

[richie4236]

I'm in the process of replacing my kitchen sink. Unfortunately the previous owner of the house was a bit of a bodger, and he didn't bother with things like isolators, which means, in order to replace the tap, I have to turn off the supply to the entire house. Obviously, as I replace the sink / tap, I will be adding isolators, but for now, I have a question about turning off the supply. I tried the main valve under the sink but it's totally jammed. I had a bad experience with one of these before, when I tried to force it, so I went out and turned off the water in the street. I also closed the valve between the cold tank in the loft and the hot water cylinder in the airing cupboard. To my surprise the water still flower, albeit very slowly, from taps in the kitchen, utility room and bathroom. It still ran too quickly to allow me to work on the pipes and install the isolators, so I gave up.

Having considered it I now think I know what was happening, and have a couple of questions.

Presumably, with the external feed shut off, the water which was coming out of the cold tap in the kitchen was the pipework draining. I'm not sure how much stuff is fed from the mains, and how much from the loft tank, but it seems reasonable to assume the cold water taps in the kitchen and utility, as well as the boiler, are fed that way. The cold water tank in the loft is fed by a ball cock, so presumably it can't be the cold water tank itself draining back down to the kitchen tap? The cold tap in the kitchen is definitely fed off the mains supply. I can trace the pipework very clearly, but it soon disappears from view and it's not clear where it goes next.

Secondly, the hot water continued to run very slowly even with the value between the tanks shut. I've read that back-pressure should hold the water in the tank, but even then you can get a little bit of flow. Is this what was happening? If I need the flow to stop completely for this work then could/should I drain the hot water tank entirely?

Expert opinions gratefully received.

 

[Burnerman]

I think you need to determine absolutely whether your street stopcock is actually working fully......the loft header tank will still fill if you depress the ball cock by hand if there’s pressure there.
As for the hot supply, I’d guess the valve between the header tank and the copper cylinder is a gate valve, with a red hand wheel? These are notorious for not sealing off too.
The hot will stop however, when the loft tank is empty, once you tie the ball cock up.
John

 

[richie4236]

I think you need to determine absolutely whether your street stopcock is actually working fully......the loft header tank will still fill if you depress the ball cock by hand if there’s pressure there.
As for the hot supply, I’d guess the valve between the header tank and the copper cylinder is a gate valve, with a red hand wheel? These are notorious for not sealing off too.
The hot will stop however, when the loft tank is empty, once you tie the ball cock up.
John

Thanks. The cylinder isolator is indeed a red-handled gate valve. It was pretty stiff, so I worked it open and closed a few times, but it's the first time I've touched it in the five years we've lived here. Interestingly, closing it and opening it appears to have fixed a long-standing problem with water pressure in our shower..... so a win there at least

I'll turn off the street supply again and see if the loft tank fills.

 

[just pumps]

Fit a short piece of copper and a hose to the iso valve out side with the valve OPEN.
Now cut the pipe with a proper pipe cutter and quickly fit the iso valve to the existing pipe. Any water will flow through the hose and out to the garden. Being as the water runs very slowly there will be next to no pressure.