Bissell Powerwash PROheat 1698?

Everything operates except the water/shampoo delivery to the carpet. The hand tools produce water fine. I've stripped the machine and cleared the tubes and the spray heads over the brushes which were blocked. Blew water through the various tubes then rebuilt the beast and, NO water. I assume that to get water to the hand brush that the pump must be operating, so I am at a loss as to why I have no water when using it in its normal operation as a carpet cleaner. Any ideas, much appreciated.