Had the same problem:
1 - Vax say - it might be an airlock - Doubtful, but they say put water into the water container, hold shampooer backwards at a 45 degree angle and run it for 5 mins with trigger depressed - Didn't work for me.
2 - Remove the brush from the underside of the machine by removing the panel that runs down the side of the main base plate - variations on a theme here for various models but all essentially the same. Behind the brush, there is a black plastic strip with tiny pin holes in it that dispense the spray of water - these can become blocked so clear them out by pushing a pin through them. Still didn't work for me.
3 - Assuming no obvious physical damage, the water feed pipes and valves may have become blocked with old shampoo debris. Put a kettleful of very hot (not boiling) water into the water tank and run the shampooer for several minutes with the trigger depressed. This worked for me.
Once the water is running, carry out (2) above to finish the job.
Finally, to avoid the problem again, each time you have finished using the machine, flush it through with clean water to clear out any sticky shampoo in the pipes.
dav19390
March 2010