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AUX-RUNTIME

Ecobee · ecobee3 Lite Smart Thermostat

Ecobee ecobee3 Lite Smart Thermostat AUX-RUNTIME Error Fix: 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

Medium severity2 fixes available✨ Free fix available
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Quick Answer

Error AUX-RUNTIME on the Ecobee ecobee3 Lite Smart Thermostat means: Auxiliary Heat Runtime Alert. The top-ranked community fix is “Test Refrigerant Charge and Inspect Compressor Operation” (hard difficulty, ~90 min, DIY cost: $0-$20). 2 community-ranked fixes available below.

Published February 2026 · 2 fixes · thermostat

Content is based on manufacturer service documentation, community repair experience, and OEM technical bulletins. Always verify with your owner's manual.Learn about our editorial standards.

When to Call a Professional

While many thermostat repairs can be done safely at home, consider hiring a qualified technician if:

  • The repair involves electrical wiring, gas lines, or refrigerant
  • You've tried the top-ranked fix and the error persists
  • You smell gas, see sparking, or notice water leaking
  • The repair requires specialized tools you don't have
  • Your appliance is still under manufacturer warranty

Average professional repair cost for this issue: $250-$400.

Other Ecobee Models with Error AUX-RUNTIME

ecobee Smart Thermostat Enhanced with Radar Occupancy Sensor and Large Touchscreen

thermostat · 2 fixes

ecobee Smart Thermostat Essential with Touchscreen Display and eco+ Smart Features

thermostat · 2 fixes

ecobee Smart Thermostat Premium with Siri and Alexa Built-In, Air Quality Monitor, and SmartSensor Included

thermostat · 2 fixes

ecobee SmartThermostat with Voice Control and Alexa Built-In

thermostat · 2 fixes

ecobee4 Smart Thermostat

thermostat · 2 fixes

Other Ecobee ecobee3 Lite Smart Thermostat Error Codes

APP-SYNC

App and Thermostat Out of Sync

2 fixes
AUX-OUTDOOR

Auxiliary Heat Outdoor Temperature Alert

2 fixes
BLOWN-FUSE

HVAC Control Board Fuse Blown

2 fixes
COOL-FAIL

Cool Not Reaching Set Temperature

2 fixes
FAN-CONSTANT

Fan Running Constantly

2 fixes
FILTER-REMIND

Furnace Filter Reminder

2 fixes
HEAT-FAIL

Heat Not Reaching Set Temperature

2 fixes
HIGH-HUMIDITY

High Humidity Alert

2 fixes

People Also Ask About Ecobee ecobee3 Lite Smart Thermostat Error AUX-RUNTIME

What does error code AUX-RUNTIME mean on a Ecobee ecobee3 Lite Smart Thermostat?
Error code AUX-RUNTIME on the Ecobee ecobee3 Lite Smart Thermostat 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
How do I fix error code AUX-RUNTIME on my Ecobee ecobee3 Lite Smart Thermostat?
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.
Is error code AUX-RUNTIME on a Ecobee ecobee3 Lite Smart Thermostat serious?
This error is rated medium severity. It should be addressed soon, but your appliance may still function in a limited capacity.
Can I fix Ecobee ecobee3 Lite Smart Thermostat error AUX-RUNTIME myself?
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.
How much does it cost to repair Ecobee ecobee3 Lite Smart Thermostat error AUX-RUNTIME?
DIY cost: $0-$20. Professional repair typically costs $250-$400. Many homeowners save money by trying the top-ranked community fix first.
What other error codes does the Ecobee ecobee3 Lite Smart Thermostat have?
The Ecobee ecobee3 Lite Smart Thermostat has 8 other known error codes, including: 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), FAN-CONSTANT (Fan Running Constantly), and 3 more.
Which other Ecobee models have the AUX-RUNTIME error?
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 Smart Thermostat Premium with Siri and Alexa Built-In, Air Quality Monitor, and SmartSensor Included, ecobee SmartThermostat with Voice Control and Alexa Built-In, ecobee4 Smart Thermostat. The fix may vary by model, so check each model's specific page for tailored repair steps.
What other error codes does the Ecobee ecobee3 Lite Smart Thermostat have?

The Ecobee ecobee3 Lite Smart Thermostat has 8 other known error codes:

Which other Ecobee models have the AUX-RUNTIME error?

Error code AUX-RUNTIME also appears on 5 other Ecobee models:

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