Thermostat shows E4 and may not control humidity or dehumidification properly

Safety: Turn off HVAC power at the breaker before removing the thermostat from the wall.

• Reboot and reset: Power cycle the system and perform a soft reset from the thermostat menu. Check if humidity reading returns to normal and E4 clears.
• Check environment: Avoid spraying cleaners or air fresheners directly on or near the thermostat. High humidity events (like painting or drywall work) can temporarily affect the sensor; allow 24 hours to dry out.
• Visual inspection: Remove the thermostat from the sub-base and inspect the vented area where the humidity sensor resides. Look for dust buildup; gently blow out with dry compressed air (short bursts, from a distance).
• Disable humidity control (temporary): In installer settings, you can temporarily disable humidity control features so the system can still heat/cool while you arrange replacement.

Note: The humidity sensor is integrated into the thermostat. Persistent E4 usually requires thermostat replacement.