Thermostat shows F3 and indicates a dehumidification or humidity sensor fault; humidity readings may be inaccurate or blank.

Safety first: Turn off power to the HVAC system before removing the thermostat from the wall.

• Verify readings: Compare the thermostat humidity reading to a known‑good portable hygrometer placed nearby. If the thermostat shows 0%, 100%, or --, the sensor is likely failed.
• Clean sensor area: Remove the thermostat and gently blow out dust from the ventilation slots using dry compressed air. Do not spray cleaners into the thermostat.
• Reset and recalibrate: Perform a factory reset from the thermostat menu. Some Payne models allow a humidity offset; set this only if the sensor is reading consistently but off by a few percent.
• Inspect internal connector (advanced): If accessible, locate the small humidity sensor module on the PCB and ensure its connector is fully seated.
• Replace thermostat: The humidity sensor is typically integrated and not field‑replaceable. If F3 persists and readings are invalid, replace the Payne smart thermostat.