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This is long saga after I used DYno (British Gas contractors) to try and replace the Stop Cock as it was faulty causing water hammering. The Dyno plumber didn't remove the old faulty stop cock and replace with another stop cock, he decide to put a quick fix in my absence. He fully jammed the stop cock in the open position. When the plumber left, I tried to make sure there was no leaks and I tried to check out if I can close the valve. I couldn't turn it by my bare hands, it was so tight. So I reached my glove and still couldn't make any movement. I then tried to use my wrench to get more leverage on the spindle. But it won't move, so this tells you what the plumber has done.
The plumber wouldn't think in a million years that I tried to turn the stop cock after he left and discovered that it was dead seized opened so exposed me to risk of inability to isolate the mains should a leak occurs in the house.
I called him back immediately and he came back and he didn't need to check the stop cock for himself to see if it can't be shut off. Instead he came straight back with a Gate valve and fitted one next to it, as the stop cock is in a permanent opened state.
I though that was the end of it, until I checked with my home insurance leak policy, it states that their should be a means of isolating the mains should a leak occur and it should be maintained (i.e. able to shut off when required) and it should be to BS standard. It was very clear to me, so I talked to the insurance to clarify the Gate Valve if it can be used in place of the conventional stop cock, the answer was no!
Now I have asked my local plumber to put things right. He removed the both the old stop cock and the gate valve and replaced with the Cronex Stop cock. Sorry for the long story.