Arrived to perform a courtesy water heater flush for customer. Upon arrival, checked water pressure and water pressure at 75psi. Went ahead and started draining down water heater. While water heater was draining noticed that expansion tank was not letting any air out. Determined that expansion tank has failed. Informed customer of findings. Customer wants to go ahead and replace it. Replaced expansion tank and set pressure to 75psi to match house pressure. Checked for leaks and no leaks detected. 1 year warranty on expansion tank.