Service diagnostic found that the upstairs primary drain line was clogged. This backed up water into the water safety switch and shut off the system. I also found the blower wheel is dirty. I spoke with the homeowner and he chose to have the drain line serviced. I cleared, flushed, and treated the primary drain and cleaned the primary pan. Verified water is draining outside. Cycled power at the thermostat. The system is operational at completion of service.