Service diagnostic found that the primary condensate drain line was partially clogged. Water was backing up into the safety switch and shutting down the system. The safety float switch is also tied into 24v power, so anytime is trips it kills power to the thermostat causing it to reset. Options for repair were presented to the customer and he chose to have the drain line cleared. I cleared the drain line and flow tested it with 2 gallons of water. I then treated the drain. The system was function checked and was running at the time of departure.