Clutch pedal has no feel and pushes to floor effortlessly; causes?

[Jonesy_sa]

An update. Finally got around to replacing the slave cylinder (cooling system etc) to get car driveable and it felt allot better for a few weeks but not perfect. I have now adjusted the push rod on the pedal right up as the clutch was not engaging until close to full release.
The clutch now engages a bit sooner but not much. Before I book it in for a clutch I want to make sure its not the master cylinder or power assist.
I've heard they can leak back into the power booster but I don't seem to loose fluid. Could it also be simply by passing within the cylinder; what's the best way to test it?