Ecobee ecobee Smart Thermostat Premium with Siri and Alexa Built-In, Air Quality Monitor, and SmartSensor Included AUX-RUNTIME Error Fix: Auxiliary Heat Runtime Alert

Error code AUX-RUNTIME on the Ecobee ecobee Smart Thermostat Premium with Siri and Alexa Built-In, Air Quality Monitor, and SmartSensor Included means: Auxiliary Heat Runtime Alert. Auxiliary/emergency heat ran for longer than the configured threshold (default 3 hours) in a 24-hour period — this indicates the heat pump may not be keeping up with heating demand, potentially due to low refrigerant, a failed compressor, or outdoor unit issues; excessive aux heat use significantly increases energy costs

The most successful fix is "Test Refrigerant Charge and Inspect Compressor Operation" (hard difficulty, ~90 minutes). Estimated DIY cost: $0-$20. HomeMD has 2 community-ranked fixes for this error.

This error is rated medium severity. It should be addressed soon, but your appliance may still function in a limited capacity.

Yes — the top-ranked community fix ("Test Refrigerant Charge and Inspect Compressor Operation") is rated hard difficulty and takes about 90 minutes. Tools needed: T20 Torx screwdriver, HVAC manifold gauge set, Multimeter, PPE gloves and goggles.

DIY cost: $0-$20. Professional repair typically costs $250-$400. Many homeowners save money by trying the top-ranked community fix first.

The Ecobee ecobee Smart Thermostat Premium with Siri and Alexa Built-In, Air Quality Monitor, and SmartSensor Included has 8 other known error codes, including: AIR-QUALITY (Air Quality Alert), APP-SYNC (App and Thermostat Out of Sync), AUX-OUTDOOR (Auxiliary Heat Outdoor Temperature Alert), BLOWN-FUSE (HVAC Control Board Fuse Blown), COOL-FAIL (Cool Not Reaching Set Temperature), and 3 more.

Error code AUX-RUNTIME also appears on 5 other Ecobee models: ecobee Smart Thermostat Enhanced with Radar Occupancy Sensor and Large Touchscreen, ecobee Smart Thermostat Essential with Touchscreen Display and eco+ Smart Features, ecobee SmartThermostat with Voice Control and Alexa Built-In, ecobee3 Lite Smart Thermostat, ecobee4 Smart Thermostat. The fix may vary by model, so check each model's specific page for tailored repair steps.