E04
Johnson Controls
Internal Humidity Sensor Failure
Thermostat shows E04 and will not control humidity; indoor humidity reading may be missing or incorrect.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Failed onboard RH sensor, Contamination from dust or paint, Condensation damage on sensor, Firmware calibration error
How to Fix / Troubleshooting
Safety: Turn off HVAC power at the breaker before removing the thermostat.
- Step 1 – Reboot and check: Power cycle the system and see if E04 clears. If it returns, proceed.
- Step 2 – Inspect sensor vents: Remove the thermostat and inspect the ventilation slots. If clogged with dust or paint overspray, gently clean with a soft brush and dry compressed air.
- Step 3 – Check installation location: Avoid mounting near bathrooms, kitchens, or other high‑humidity sources that can condense inside the thermostat. If necessary, relocate the thermostat.
- Step 4 – Factory reset and recalibrate: Perform a factory reset. If your model supports humidity calibration, compare to a known good hygrometer and adjust within the installer menu.
- Step 5 – Replace thermostat module: If E04 persists, the internal humidity sensor (integrated on the PCB) has failed. Replace the thermostat display/control module or entire thermostat.
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Repair Difficulty
Medium
3/5
Required Part
Thermostat Display/Control Module (Humidity Sensor)
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