Came out to perform preventative maintenance on furnace for customer. Discussed with customer about maintenance, filters, and how the system has been doing overall. Customer stated the filters were due to be changed, and he ended up taking care of it while I was completing the service. Discussed water filtration and flushing hot water tank. Customer has flushed his tank himself before and plans to do it again. Inspected the blower assembly, motor, capacitor, electrical components, heat exchanger, evaporator coil, burners, flame sensor, igniter, gas valve, inducer motor and overall condition of furnace. Heat exchanger has no signs of cracks at this time. Hot surface ignitor is reading 80.5 ohms, so I made customer aware that the part may fail soon. I checked thermostat operation, wiring, amps, temperatures and gas pressure. Cleaned the flame sensor properly and cleared out inducer port. Static pressure was within range during heating operation. Dropped from .52 to .45 when customer chan