Typically, the pump will sound much louder than when pumping normally against pressure. Looking at the discharge point of the pump or tubing is a 100% sure way to check for pumping. Non-moving pockets of air in the suction or discharge line is another good way to tell whether or not there is chemical moving. The easiest way, solving most of the problems at the same time, is to open up the Manual Air Vent and check that the pump is pumping out the air vent.