Please inspect the exhaust hose for any bends, kinks, or full bellows extension. Normally, at the end of the run, air is taken from the hole in the middle of the exhaust hose as the chamber pressure equilibrates to atmospheric pressure. However, if there are any bends in the exhaust hose, it will prevent air flow. Please reinsert the exhaust hose so that it is not bent and replace the bellows assembly if necessary. Replacement bellows assembly for ES-315 or ES-215 can be purchased here.