Either your belt has stretched beyond its specs or you have larger problems. Are you talking about a new belt? If not, try a new belt. If so, check to make sure the beater bar will spin freely without a belt attached. If it spins without a belt attached, make sure the bearing blocks at both ends are in good shape.
You would see if you warped the tank, the issue is most likely related to melting some of the thin pump parts or tubing in the unit. Bissell does not sell those parts to the public. Find a repair center or send it in unless you want to buy a new one. PS in the future don't put high temp water in the tank, put it on the spot you are trying to clean and then vacuum it up.