If the homeowner has a bad sensor, the PureAir S unit will continue to work as intended and will only lose the visibility of the S30/A40 filter & UVA bulb life. They will have to switch to the manual timer reminder for filter & UVA bulb replacement. We recommend an annual replacement for these items. For Use With: PCO3S-14-16 (Y8905); PCO3S-16-16 (Y8904); PCO3S-20-16 (Y8903) Includes Main Sensor Board UVA Sensor Board 4 Pin Wiring Harness (2) Barbed Elbow Connector (5/32" ID) (4) Standoffs Tubing 3/4" Length - Black with Red Stripe Tubing 3/4" Length - Black with Blue Stripe Install Instructions 507817-01