Cistern overflow/leak


Hello all,
the aforementioned toilet is now installed and is leaking! It is a BIIO cistern (actually a B&Q 'Toilet to go' which is a close-coupled cistern) which leaks into the pan so it's not disastrous. It is not overflowing through the top of the overflow pipe as that is several cm above the water level. My best guess is that the flush valve has not seated with the seal washer and/or lock nut correctly and is leaking that way.
Should I remove the cistern and tighten the valve? (I think I have tendency to under-tighten such things, due to a fear of over-tightening!) The cistern does not appear to be leaking externally at all. The area around where the cistern and pan meet are dry, as is the floor.
Is there anything else I should check for? Does anyone know of an online diagram explaining precisely how these flush valves work? Suffice it say that the enclosed documentation is of little help.
TIA as ever, Pete
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Halloway wrote:

It looks like the seal is leaking. I was able to remove the flush valve mechanism such that I can now see the connection between the cistern and the pan and there is a definite leak from the back of the pipe - I can see the dripping. It's quite a substantial leak and I am wondering if I simply forgot to tighten up the lock nut at all or whether a bit of foreign matter is preventing a good seal. The water is not flowing through the outlet but it coming from 'behind' the seal (if that makes sense.) If I rotate the overflow bit that's left in the cistern, the leak moves with it.
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Halloway wrote:

Does it have a separate overflow pipe or does it overflow through the top of the siphon? If the latter, adjust the ball valve so the level is lower & it should stop. Most modern siphons have built in overflows.

Sounds more like an internal overflow. Any leak between cistern & bowl usually only happens when the cistern flushes into the toilet.
If lowering the water level doesn't work, it could be where the siphon is connected into the cistern - the big nut. Buy a tube od Fernox LS-X (B&Q) & smear liberally around both faces of the big rubber washer, leave for an hour.

Oh what a surprise :-)
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Dave - The Medway Handyman
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The Medway Handyman wrote:

Thanks for the tips. As mentioned in a previous post, the leak does appear to be at the big nut so I'll try what you suggest. When you say 'leave for an hour' do you mean 'leave for an hour and then re-assemble?'
Thanks, Pete
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Halloway wrote:

Sorry, apply, asemble, wait an hour before flushing.
LS-X sticks to wet surfaces but needs an hour to set properly.
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Dave - The Medway Handyman
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