Bissel pro heat 12 amp tank won't dispense water?

What would make the tank not dispense water ? This isnt a sprayer issue, we know it's the tank, just not sure what the problem is or how to possibly fix it. Any help or advice would be greatly appreciated !

My sister & I both have the exact same carpet cleaner - Bissel Pro heat, 12 amp, 6 row brushes, purple upright (we bought at the same time). My sister's wouldn't spray, so she borrowed mine. This was just after my after husband had taken it completely apart to clean the heater core & lines- was working perfectly. Hubbs goes to get ours , gets it home, wont work, realizes he grabbed wrong one. Goes back grabs ours. Since the tanks were already full for the 1st machine, he just swapped them out . Machine wont spray. Hubbs is furioud since it worked perfect prior to loaning it out. He checks & tries everything and gives up. Goes to empty the tanks and decides to fill OUR tanks and give it a shot- works perfectly. SO , we realize that obviously, theres an issue with her tank since it wouldnt work on either machine.