ecobee premium keeps using my expensive aux heat instead of the heat pump, how do i stop that?

Diagnosis

The ecobee SmartThermostat Premium is designed to maintain a tight temperature glide, but by default, its "Auxiliary Heat" logic is often too aggressive. This happens when the thermostat detects that the heat pump cannot raise the indoor temperature fast enough to meet the setpoint, or when the outdoor temperature drops below a pre-defined threshold. Instead of letting the heat pump run longer, the ecobee triggers the auxiliary heat strips (which are resistive and significantly more expensive to operate) to "assist" the system. You can confirm this is happening if you see the "Aux Heat" icon active on your display while the heat pump is also running, or if your electricity bill spikes during mild winter days. This is typically caused by a "Compressor to Aux Delta" that is set too low (often 2°F or 3°F), meaning if the room is just a few degrees below your target, the expensive backup heat kicks in regardless of whether the heat pump is actually capable of doing the job.

How to Fix It

To stop the premature engagement of auxiliary heat, you must manually override the staging thresholds to give your heat pump more "room" to operate before the backup heat is summoned.

1. Wake the thermostat screen and press the Main Menu (three horizontal lines).
2. Select Settings, then navigate to Installation Settings.
3. Select Thresholds.
4. Find the option for Configure Staging Manually and toggle this to Enabled. This unlocks the specific temperature offsets that are usually hidden behind the "Automatic" logic.
5. Locate Comp to Aux Delta. This value represents the temperature difference between the setpoint and the actual room temperature that triggers the aux heat. If it is set to 2°F, change it to 4°F or 6°F. This forces the heat pump to work harder and longer before the aux heat is allowed to turn on.
6. Next, locate the Aux Heat Max Outdoor Temp setting. This is the outdoor temperature above which the aux heat will never run. If your heat pump is efficient down to 25°F, set this value to 25°F. This prevents the strips from firing during a "chilly" but not "freezing" day.
7. Save the settings and return to the home screen.

If That Didn't Work

• Verify the O/B Reversing Valve Setting: If your heat pump is blowing cold air while the aux heat is running, your reversing valve is configured incorrectly. Go to Installation Settings > Equipment > Heat Pump and toggle the O/B setting. If it was set to "O", change it to "B" (or vice versa). If the valve is wrong, the ecobee thinks the heat pump is failing and will trigger aux heat to compensate for the lack of warmth.
• Check the Heat Pump Stage 2 Logic: If you have a two-stage heat pump, ensure the ecobee is not skipping Stage 2 and jumping straight to Aux. In Installation Settings, verify that your equipment is listed as a 2-stage heat pump rather than a 1-stage. This allows the system to increase compressor capacity before resorting to electric strips.
• Calibrate the Remote Sensor: If you have a SmartSensor in a cold drafty hallway, the ecobee may be averaging that cold temp with the main unit, triggering a "low temperature" state that activates aux heat. Go to Sensors and remove any sensors located near exterior doors or vents from the "Heat" participation list.
• Inspect the Wiring at the Backplate: Ensure the AUX wire (usually orange or white) is seated firmly in the terminal. A loose connection can occasionally cause "ghost" triggers or intermittent short-cycling of the heat strips.

Heads Up

• Avoid Extreme Deltas: While increasing the Comp to Aux Delta saves money, setting it too high (e.g., 10°F) may lead to "cold streaks" where your home feels chilly for hours before the backup heat finally kicks in.
• Filter Maintenance: A clogged air filter reduces airflow, which tricks the thermostat into thinking the heat pump is underperforming, triggering the aux heat more frequently. Change your 20x20 or 16x25 filter every 30-90 days.
• Outdoor Sensor Accuracy: The ecobee relies on internet weather data. If your home is in a valley or a microclimate where the actual temp is much lower than the reported "city" temp, the Aux Heat Max Outdoor Temp setting may not behave as expected.