E03
Bosch
Internal Temperature Sensor Failure
Thermostat displays E03 and cannot detect the indoor temperature sensor; temperature reading is blank or shows dashes.
Advertisements
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.
Advertisements
Possible Causes
Open circuit in internal NTC temperature sensor, Damaged sensor leads on thermostat PCB, Overheating or moisture damage inside thermostat, Manufacturing defect of sensor element
How to Fix / Troubleshooting
Safety: Turn off power to the HVAC system at the breaker before removing the thermostat from its wall plate.
- Power cycle: Turn off the breaker for 1 minute, then restore power to see if the error clears.
- Inspect mounting: Remove the thermostat from the wall plate (if it has a detachable front) and check for obvious moisture, corrosion, or physical damage. Do not touch the PCB components.
- Check location: Ensure the thermostat is not installed directly above a heat source or in direct sunlight, which can overheat the internal sensor and trigger faults.
- Reset to defaults: From the settings menu, perform a factory reset (note: this will erase schedules and Wi‑Fi settings). Reconfigure and see if the sensor is recognized.
- If E03 persists: The internal NTC sensor or PCB is likely defective. Replacement of the thermostat assembly is usually required.
Advertisements
Repair Difficulty
Medium
3/5
Required Part
Bosch Smart Thermostat Main Control Assembly
Check Price on Amazon
We may earn a commission from links on this page.
Advertisements