nest e installed but it says my system is only single stage when i know my heat pump has auxiliary heat

Diagnosis

The Nest Thermostat E is utilizing an automated detection system during the initial "Equipment" setup phase. In many cases, the device fails to correctly identify the presence of a secondary heat source—such as electric heat strips or a backup gas furnace—because the voltage on the AUX/W2 wire is not active during the installation scan. This results in the thermostat defaulting to a "Single Stage" configuration, which means it will only trigger the compressor's heat pump cycle and completely ignore your auxiliary heat strips during extreme cold. This mismatch typically happens if the thermostat was configured as a "Conventional" system instead of a "Heat Pump" system, or if the "Heat Pump" option was selected but the secondary heat source was set to "None." You can confirm this by checking the "Equipment" display in the settings menu; if you see a wire connected to the AUX terminal on the back of the device but the software screen shows that terminal as empty or unused, the software configuration is the root cause.

How to Fix It

You must manually override the automatic detection and reconfigure the equipment profile to recognize the auxiliary heat. Follow these exact steps:

1. Press the thermostat display ring to open the main menu.
2. Rotate the ring to Settings and press to select.
3. Scroll to Equipment and select it.
4. Select Equipment Display to verify which wires the Nest thinks are connected. If the AUX wire is not highlighted, you must select Reset or Change Equipment.
5. When prompted for the system type, select Heat Pump. Do not select Conventional, as this will disable the reversing valve logic.
6. When asked about your fuel source, select the specific type your auxiliary heat uses (e.g., Electric for heat strips or Gas/Propane for a dual-fuel setup).
7. The device will then ask if you have auxiliary heat. Select Yes.
8. The Nest will now map the W2/AUX wire to the secondary heating stage. Confirm that the "Auxiliary Heat" option is now listed in the equipment summary.
9. Save the settings and allow the device to reboot the HVAC interface.

If That Didn't Work

• Verify the C-Wire Connection: The Nest E is notorious for "power stealing" from the Rh/Rc wires. If you do not have a Common (C) wire installed, the thermostat may not have enough consistent power to trigger the auxiliary relay, causing it to report the system as single-stage. Install a Nest Power Connector or a dedicated 24V C-wire to stabilize the voltage.
• Check the O/B Orientation: If your heat pump is blowing cold air when it should be heating, your O/B setting is reversed. Go to Settings > Equipment > Heat Pump and toggle the O/B wire from "O" to "B" (or vice versa). This is common with Ruud or Rheem units which often use the "B" setting.
• Inspect the W2/AUX Wiring: Ensure the wire is stripped exactly 3/8 of an inch and inserted fully into the terminal. If the wire is loose or the copper is oxidized, the Nest will not detect the circuit and will default to a single-stage configuration. Use a multimeter to check for 24V between R and W2 at the wall when the system is calling for heat.
• Perform a Factory Reset: If the equipment menu is glitching and won't let you change the fuel type, go to Settings > Reset > All Settings. This clears the cached hardware detection and forces the Nest to run the setup wizard from scratch.

Heads Up

• Aux Heat Threshold: Be aware that Nest uses a "Heat Pump Balance" logic. It will not engage auxiliary heat unless the indoor temperature drops significantly below the set point or the outdoor temperature is extremely low. Do not assume the fix failed just because the heat strips don't turn on immediately.
• Dual-Fuel Logic: If you have a dual-fuel system (Electric Heat Pump + Gas Furnace), ensure you have selected "Dual-Fuel" specifically. This tells the Nest to disable the heat pump compressor once the outdoor temperature reaches the "lockout" threshold to prevent efficiency loss.
• Voltage Warning: Never attempt to connect a 120V or 240V high-voltage wire to the Nest E. This thermostat is strictly for 24V low-voltage systems; connecting high-voltage lines will instantly fry the base plate and void your warranty.