Low water pressure and stop tap?

Can a stop tap fail?
I have a problem with low water pressure/flow in my house. The problem is at the stage that if two taps are opened at the same time, water does not flow at all out of one tap.
Pressure in the street is OK - neighbours have no problem, and stop tap in the street in fully on.
The stop tap in the house appears to be in the cellar (cast pipe to copper half buried in the wall), however turning it makes no difference at all either way. I therefore suspect that the stop tap is not for the water?
Is it possible for a tap (stop tap rather than gate valve) to fail completly.
Any ideas what else the problem could be?
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Hello Simom

Yes.
on/off are ambiguous - I take it you mean fully open?

Or that's the one that's failed.

They generally fail in one of the following ways:
1. Shaft siezes or snaps - can't move it.
2. Stop cock washer disintegrates meaning the stop cock fails to turn off the water.
3. Stop cock washer disintegrates and blocks either the pipework further on, or within the cock itself.
4. Your pipework (anything after the street stop where it enters your boundary line) has a serious leak.
I suspect 3.
To fix; Turn off water in street cock.
Take apart your inside stop cock and check washer. If it's all there, remove and replace. If it's shot off somewhere else, replace the washer anyway and have fun finding out where the last one went - it'll probably be wedged at a joint somewhere down the line. Useful to grease the shaft while you've got it apart too. DON'T OVERTIGHTEN THE TAP WHEN YOU REPLACE IT!
It could be the street cock that's failed. That's the water company's problem, but don't tell them until you're reasonably happy its not your own pipework that's at fault, or they'll probably charge you a callout fee.
--
Simon Avery, Dartmoor, UK
uk.d-i-y FAQ: http://www.diyfaq.org.uk /
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