My Bissell proheat will not dispense soap when the trigger is pressed. I have taken this thing apart from top to bottom and can't find anything wrong with it. I have even used my shop vac to blow into the soap dispensing hole while on water only at the same time i am vaccumming out the hole where the red spinner is. When i vaccuum it out it will spray but when i turn the soap dispensing knob to high traffic or the medium setting it stops working after a few seconds. I have reversed the blow/**** thinking there might be debris in the line and it works for about 20 seconds or so but then won't work again. I love this cleaner but am thoroughly disgusted with its performance at the present time. Please help

Vacuums - Bissell - 7901-1 ProHeat Scotchgard Upright Wet/Dry Vacuum