Why Does My Ecobee Keep Running Auxiliary Heat Instead of Heat Pump?
- Aux Heat Max Outdoor Temp set too high allowing aux at warm temps
- Compressor Min Outdoor Temp set too conservative for your heat pump
- Heat pump cannot keep up with setpoint differential calling aux early
Problem Description
Your Ecobee thermostat is using expensive auxiliary heat constantly instead of your more efficient heat pump causing high electric bills. The Aux icon shows on the thermostat display even when outdoor temperatures are moderate enough for the heat pump to handle the load.
Symptoms
- Aux heat icon showing constantly on Ecobee display
- Heat pump not engaging even in moderate cold weather
- Electric bill spiked dramatically after installing Ecobee
- Ecobee using aux heat when outdoor temp is above 40 degrees
- Heat pump runs briefly then switches to aux heat
- Compressor Min Outdoor Temp threshold set incorrectly
Recognize these? Here's what usually causes it.
Common Causes
- Aux Heat Max Outdoor Temp set too high allowing aux at warm temps
- Compressor Min Outdoor Temp set too conservative for your heat pump
- Heat pump cannot keep up with setpoint differential calling aux early
- Threshold settings not optimized for your climate zone
- Heat pump low on refrigerant reducing efficiency triggering aux backup
- Wiring incorrect during installation with W1 instead of W2 for aux
Most fixes happen in the first 3 steps.
Setting Compressor Min Outdoor Temp too low can damage some heat pumps by forcing them to run in temperatures below their design range. Check your heat pump manual for true operating limits.
Tools & Requirements
These tools will help you complete this fix.
Ecobee thermostat
Thermostat Lock Box Cover with Key – Secure Lock Box...
Heat pump model specifications
PRO1 T855iSH 8” Backlit WiFi Thermostat, 7-Day Progr...
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Step-by-Step Solution
Check Your Heat Pump Specifications
Find your heat pump model number on the outdoor unit. Look up the minimum operating temperature in the specifications. Standard heat pumps operate down to 25 to 35 degrees Fahrenheit. Cold climate heat pumps operate down to 0 to minus 15 degrees. Ecobee should only call aux heat below your heat pump minimum. Note this temperature for the next configuration steps.
Needed for this step
Thermostat Lock Box Cover with Key – Secure Loc...
$16.99Adjust Compressor Min Outdoor Temp
On Ecobee go to Main Menu then Settings. Tap Installation Settings then Thresholds. Find Compressor Min Outdoor Temp setting. Set this to your heat pump actual minimum operating temperature. Do not set it conservatively high or aux heat runs unnecessarily. For standard heat pump set around 30 to 35 degrees.
Needed for this step
PRO1 T855iSH 8” Backlit WiFi Thermostat, 7-Day ...
$162.70Lower Aux Heat Max Outdoor Temp
In the same Thresholds menu find Aux Heat Max Outdoor Temp. This is the highest temperature at which aux is allowed to run. Set this 5 to 10 degrees above your Compressor Min Outdoor Temp. If aux runs when it is 50 degrees outside this setting is wrong. Lower it to around 40 to 45 degrees for most climates. This prevents aux from engaging in moderate weather.
Verify Heat Pump Wiring
Go to Settings then Installation Settings then Equipment. Tap Wiring to see the wire configuration. Your heat pump should be on Y1 terminal. Reversing valve should be on O/B terminal. Auxiliary heat should be on W2 or Aux terminal. If aux is on W1 the system thinks you have a furnace not heat pump.
Quick Solutions
Still having issues? This is usually the deeper cause below.
If this comes back after following these steps, check whether a recent app or firmware update reset a default setting — the fix works, but the setting gets reverted silently.
Set an Aux Runtime Alert under Thresholds to notify you if aux runs more than 2 to 4 hours. This helps identify when aux usage is excessive so you can investigate.
This issue almost always looks more complex than it is — the majority of cases trace back to a single setting, a stale credential, or a default that shipped wrong.
- Aux Heat Max Outdoor Temp set too high allowing
- Compressor Min Outdoor Temp set too conservative for your
- Heat pump cannot keep up with setpoint differential calling
- Threshold settings not optimized for your climate zone
- Heat pump low on refrigerant reducing efficiency triggering aux
Before you go — try one of these (they fix most cases).
Most popular upgrades chosen by Ecobee Smart Thermostat owners.
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Official Manufacturer Manual
Ecobee provides official product documentation through their online manual rather than downloadable PDF. Access setup guides, troubleshooting steps, and product specifications for your Ecobee Smart Thermostat.
Source: ecobee.com
Need More Help? Ecobee Support
Note: The contact information below connects you directly to Ecobee's official customer support team, not Trunetto. They can help with warranty claims, device replacements, and advanced technical issues.
How Does Ecobee Compare?
Before replacing your Ecobee device, see how it stacks up against alternatives in our full comparison guides.
