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Ecobee - ✅ Safe to Use

Ecobee - Error Code AUX

Ecobee Thermostat error code AUX: Auxiliary heat active.

Last reviewed: Last updated:

Methodology: We combine OEM HVAC documentation with field repair patterns, then review for safety-first troubleshooting.

Sources: HVAC manufacturer documentation, installation/service manuals, and technician-reported repair patterns.

Limits: Guidance is informational and may not match every model-year or revision. Confirm with the official manual and diagnostics before replacing parts. For safety-critical or electrical work, use a qualified technician.

Is it safe?
✅ Safe temporarily
Safe to use on cold settings temporarily. Heating element failure is a common DIY repair.
Can I fix it?
DIY Possible
Tools: Multimeter, Screwdriver set, Nut driver
Repair cost
DIY: $20–$100 (element or thermistor)
Pro: $100–$300
⏱ 30–60 min

What Does Error Code AUX Mean?

Ecobee Thermostat error code AUX: Auxiliary heat active.

Part that typically fails: Heating element / thermal fuse / thermistor

Safe to use on cold settings temporarily. Heating element failure is a common DIY repair.

Symptoms You May Notice

Troubleshooting Steps

  1. 1 Check your owner's manual for model-specific guidance on error code reset procedures
  2. 2 If the error persists after reset and basic checks, contact a qualified technician
🛠️ Tools needed: Multimeter, Screwdriver set, Nut driver · Time: 30–60 min
⚡ Quick tip: Always try a full power reset first — turn the unit off at the breaker, wait 30 seconds, restore power.

Frequently Asked Questions

What does Ecobee Thermostat error code AUX mean? ▼
Error code AUX on a Ecobee thermostat indicates: Auxiliary heat active. The unit has detected this condition and has limited or stopped operation to prevent further damage.
How do I fix Ecobee Thermostat error code AUX? ▼
Start by powering the unit off for 30 seconds and restarting. If error AUX returns, the underlying cause (auxiliary heat active) needs to be addressed. Check wiring connections and filters first before replacing components.
Is Ecobee error code AUX serious? ▼
It depends on the root cause. Some AUX errors resolve with a reset. Others indicate a failed component that requires professional repair. Don't continue operating with this error — it can lead to further damage.

More Ecobee - Error Codes

All Ecobee - codes → All Ecobee HVAC codes →

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