Toilet supply pipe leak

I have a problem with a leak from the supply pipe to a toilet that I would appreciate some help with. You can find a picture at
http://www.butterflyguy.com/toilet1.jpg . It is a problem at the in flow to the ball valve.
Initially there had been a very slow leak from the nut which I noticed when I moved in. It was only a slow drip and could be easily ameliorated by putting a trough underneath and turning off a stop cock when if I left the place empty for a few days. One of those awkward jobs that I could put off.
However, it got worse recently spraying a fine mist onto the wall behind. It is apparent that the cistern was replaced some time ago and the plastic ball valve assembly had not been properly fixed into the supply. Looking at it the thread had been damaged and this could have been the source of the leak.
I got a new metal ball valve assembly and tried to fit it.
The problem is that I can't form a seal at all. As soon as I turn the pressure on the water jets out of the back of the nut. (See the arrows in the picture)
The nut is only hand tightened and I suspect was never turned at all when the cistern was replaced because paint, which seems to have been applied earlier from the decor of the room, came off. I doubt I could tighten it much further. Or am I wrong and this is the source of the problem?
The nut, by the way, turns fairly freely but does not come off at all.
What do I need to do?
Neil Jones snipped-for-privacy@nwjones.demon.co.uk
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Neil Jones wrote:

The joint between the blue nut and the new ball valve should have a fibre washer between the flange on the pipe and the ball valve inlet. I suspect this is missing. Your plumbers merchant should be able to supply one otherwise buy the cheapest tap connector which will have one included with it.
hth
Bob
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On 22 Oct 2003 11:50:32 -0700, snipped-for-privacy@nwjones.demon.co.uk (Neil Jones) wrote:

Unfasten it all and wrap some PTFE tape on all the threads. A few turns is all you need then tighten them back up, would have thought the one in question would need tightening with a spanner as well.
Mark S.
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On 22 Oct 2003 11:50:32 -0700, snipped-for-privacy@nwjones.demon.co.uk (Neil Jones) wrote:

That assembly looks to be at an angle as it enters the cistern. The white lock nut on the cistern side clearly isn't tightened up. What this suggests to me is that the blue feed pipe is possibly taking the weight of the assembly, and that would tend to stress the water joint.
The valve assembly should be self-supporting before you attach the water feed pipe on the outside - by tightening the white lock nuts either side of the entry into the cistern.
The other thing is that you have an olive under the nut (that's the painted nut). If that joint has been tightened and released a few times then the olive probably needs replacing - you'll need to hacksaw off the existing one very carefully so as not to damage the pipe.
As Bob Minchin advises, you should have a fibre washer inside the nut on the inlet side, these are sold in packs of 5 or 10 in the DIY sheds. The fibre washer compresses very slightly to form a seal when the nut is tightened up.
What I'd be tempted to do with that water feed pipe is chop it off and put on a new section. If you haven't got an isolation valve on that feed it would be sensible to add one anyway. That way you can turn the water off for just the cistern without having to turn off the house supply followed by draining the system!
PoP
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You've actually got the wrong type of valve: you should have one where the water comes out of a little plastic spout above the body of the valve (attempted ascii art follows). This is a water regulations issue about preventing backflow (water getting sucked back into the mains if the mains pressure fails) rather than a show-stopper (as in it wouldn't work).
_______ / \ | ____ | spout ______||___ | | _____ //////| | / \ valve | / \ //////| |o----------------------------| ball | |___________| \ / \_____/

Either, as Bob Minchin suggested, it's a tap connector which needs a fibre washer or as PoP suggested it could be a compression fitting (less likely, I think, from your photo). If the connector bit has what looks like a square section metal washer formed on the end of the pipe it's a tap connector, if there's a wedding ring-type piece of metal on the pipe that's an olive. You rarely need to remove and replace an old olive - a bit of sealing material such as Boss White or Boss Green or silicone should help seal it up. Fibre washers, on the other hand, do need replacing. Sometimes the remains of the old one get jammed in the threads of the nut and you have to dig it out with something like a compass point.
After you've got the connector onto the float valve, then tighten the big white nuts to hold the valve firmly onto the cistern, then fully tighten the connector to the float valve. (This order of things is more important with plastic-threaded float valves which are very easy to strip the threads off with a metal connector.)
-- John Stumbles -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -+ Load dropped, paperwork completed: job done.
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