I am having what seems like an identical problem. Advice on the net is: If you can disconnect the plastic tube from the back of the Push button and blow a little down it and it flushes, then the good news is it is probably just the Push Button unit. I was able to unscrew my push button off and pull it to pieces (about 3 mechanical components). I found that the Rubber/neoprene bellows had a crack in that meant even though it sounded like it was working it was expelling air out the wrong place.
2 solutions if you find a crack, one quicker than the other. Firstly, if you have B&Q rubber glue, stick some on the hairline crack and dry with a hairdryer. Re assemble the bellows to the tube and give it a puff to see if you have fixed the symptom. If so reassemble and tell the wife and kids the loo is "tolerably in Service". The bellows will need replacing soon I would suggest. Whilst doing this get any manufacturing or serial numbers and ring a local Plumbing merchant. In my case I rang the manufacturer directly with a part number and explained the fault, the nice chap on the phone is sending me out a new bellows first class.
AndyB, January 2009
