Fordham flushpanel syphon - not fully flushing

[balloney]

My toilet does not fully flush.
I have taken the Fordham Syphon out and cleaned it, all looks ok.
The two flaps underneath are undamaged.
I am stumped as to why it does not fully flush.

Help please.

[The Builder]

I think that's the "older" type of syphon. They have a simple plastic diaphragm. This can get a bit weak and floppy with age (ooo-er)
In the past, the usual thing was to cut a new one out of some heavy polythene damp-proof membrane.
Google it, and you'll find replacement syphons are available. Not sure about the diaphragm though.
It really is a simple DIY job to fit a modern unit instead.....

Just pick one out of this lot ....

http://www.screwfix.com/search.do?fh_search=flush&fh_view_size=20&fhSearchParams=fh_location%3D%2F%2Fscrewfix%2Fen_GB%2F%24s%3Dflush%2Fsegment%3D%7Bscrewfix%7D%2Fcategories%3C%7Bscrewfix_cat830950%7D%26fh_refpath%3Dfacet_87316993%26fh_eds%3D%25C3%259F%26fh_reffacet%3Dcategories%26fh_refview%3Dsearch&fh_sort_by=&customPrice=&priceFrom=&priceTo=&priceFilterOn=&_requestid=1428985

[alavahalf]

There tends to be two reasons why a toilet does'not flush properly.

The water level is not high enough in the cistern ..

And secondly as previously stated by TB ... the diaphragm becomes damaged or split.
I find the most common fault is the split. Making your own using the original as a template is the easiest way to get it right. Heavy duty polythene is the preffered material.