A simple test to verify that your heater is functioning is to place your hand above the unit. There should be cool air blowing out of the top after approximately a 2-3 minute time delay. The water returning to the pool should be a few degrees warmer than water entering the heater. After about 15 minutes of run time, there should be water draining out of the base of the unit. If you have reason to believe your heater is not functioning properly, follow the troubleshooting guide link below or call 239-567-0009 Ext 1 for service.