Toilet won't flush

[spezza123]

Just moved into a new flat and the toilet doesn't flush. Sometimes it takes about 10-20 turns of the handle until it does. Been reading up on how a toilet works and I think my problem may be that I need a new syphon. When I took the lid off I noticed that only some water makes it into the top of the big plastic upside down u. When it finally does flush the water is continually flowing through this upside down u until flush is over. The water level in the cistern is fine and there are no leaks or overflows. Do i just need a new syphon and are they easy to repacle. Seems like a case of unscrewing the old one and puttin in new one Thanks

[New Forester]

More likely it's just the valve which has gone. This is usually a flat sheet of plastic shutting against a plastic grid, and eventually it splits and stops working properly. You may be able to get a new valve, or even make one, but you may find you're stuck with getting a new siphon anyway. If you have the kind of cistern where the inlet is beneath, make sure you get the seals perfectly clean before reassembly or it'll leak.