check pressure switch, for a split pipe, or more likely a blocked pressure chamber hole 
remove top of machine locate the pressure switch  round thing with wires and a plastic pipe remove the pipe from switch and check for any possible splits where it could rub the casing if OK blow down the pipe if you go red pipe is blocked ,follow and  locate the other end of the plastic pipe and  remove, now clear the blocked hole with a stiff piece of wire
blow up the pipe and you should hear the switch click 
reassemble the pipe end and allow machine to fill.
                
 wirecutterman
                
 February 2009