Planning to fit ball valve to cold water tank feed

30 May 2007
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United Kingdom
Some time ago I fitted ball valves in line to poor performing gate valves, feeding the bathroom from a cold water tank in the loft and hot water storage cylinder. I emptied the cold water tank in the loft.

The ball valve to the cold water feed bathroom taps went in fine.

However for the cold water feed to the shower, I was not able to stop a flow of water out of the shower head. Obviously I didn't fancy cutting in to the pipe so I remember partially dismantling the gate valve and water came gushing out. The gate valve is about 30cm (12inches) higher than the mixer for the shower and runs vertically directly down from the tank in the loft.

I wondered if there was an amount of water in the cold water shower loop that is always "stuck" there. Is it a simple case of having a bucket and towels handy and then dismantling the gate valve prior to cutting and fitting the ball valve?

I plan to replace the shower unit soon so wanted to get that ball valve in second time round!

Any advice appreciated.
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If you drained the loft tank there should be no water feeding the shower valve ,and lowering the shower head should drain water from it . Where exactly is the gate valve ,in height ,relative to the shower valve and any fixed shower head ?
Thanks Terry. There is no fixed shower head, I recall lowering the shower hose in to the bath so couldn't work out why I was getting a flow when the water tank was drained. The gate valve is 30 cms higher than the shower mixer. Defies the laws of physics. I'm taking it again in a couple of weeks, complete with bucket and towels as backup.
Was the water flowing at full pressure or just a dribble ?
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It was a dribble but I was wary non-the-less so didn't cut in to the feed, that's when I loosened the gate valve and found water coming out. In the end I tightened all back up and left it for another day! I'm hedging on undoing the gate valve with a bucket handy.
I wonder if the domestic hot water is finding its way into the cold via the shower valve ,is it a thermostatic mixer?
Last time did you drain the hot ??
Yes it is a thermostatic mixer shower (Aqualisa 1996 model). The hot water cylinder was drained at the time as I had fitted a ball valve to that feed too (no problems).
Cant be more than a bit of residual water held in pipe run if you did all that.
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