Close-coupled cistern. I've just replaced the syphon and I've got leak problems. There are no bolt holes in the cistern, it uses a steel plate beneath as a doughnut compressor.
How many thin rubber washers should be used? Obviously one is beneath the syphon on the inside. Are others required around the steel plate, or should the doughnut alone be sufficient?
Should be just the doughnut. If the seal between the siphon and the cistern is leaking you will have a constant dribble - if it only leaks when you flush its the seal between the cistern & the WC - the doughnut.
Usually one rubber washer between base of syphon & hole in cistern - I always liberally LS-X that.
There are two types of 'doughnut', one is square section & t'other is rounded over on the bottom face. You have to replace like for like.
You did fit a new doughnut? They never work if you re use them.
Also - make sure the bolts are threaded all along their length - some of the 'kits' available (Homobase) have partly threaded bolts & you can't tighten them enough.
If a new doughnut don't not sort it, Plumbers Mait is the answer. Don't use silicone, it just makes a mess.
HTH
Probably teaching my granny, but make sure the new syphon is nicely centred and flat. I had no end of trouble with leaks last time I replaced one, because the silly cramped cistern only just had room for the new syphon and a Torbeck valve, and each time it got flushed the syphon pulled a little further off centre. It tested OK each time I re-fitted it but the leak just got worse. Eventually had to replace the Torbeck with a good old ball valve so the syphon could sit straight !
Nick
I think that was the trouble in the end. It's a nasty old '70s cistern & pan (double syphonic!) and has a vast hole in the bottom of it. The syphon had shifted sideways a bit and there was no good contact at the edge of the rubber washer.
I put it back together with a spare O ring dropped loosely over the syphon to hold it central. Now it seems OK and leak free.
Now I just need to wait for the cement patch in the wall to cure before I can screw it back onto the wall properly. The thing has been on and off so many times that the old wooden plug has fallen apart and the hole has broken out bell-mouthed 8-(
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