Performed preventative maintenance on Furnace for customer. Changed out power guard filter. Inspected the blower assembly, motor, electrical components, burners, flame sensor, igniter, inducer motor and overall condition of equipment. Checked thermostat operation, wiring, amps, temperatures and gas pressure. System is heating properly within manufacture specifications. UV Bulbs were at the end of their life span. Recommended replacing them before they go out. Customer approved replacement. I replaced both bulbs and tested them to verify they were both working. Bulbs have a 2 year lifespan.