AUX heat, or auxiliary heat, is a backup heating system that supports a heat pump during extremely cold temperatures or when the primary heat pump cannot keep up with demand. If AUX heat isn’t working, you may notice your home isn’t warming up as expected, or your system runs inefficiently. Here’s how to troubleshoot and fix AUX heat issues.
1. Check Thermostat Settings
- Ensure the thermostat is in Heat mode.
- Increase the set temperature by 2-3°F above the current room temperature to activate AUX heat.
- Test the Emergency Heat mode (if available) to determine whether the backup heating system is functional.
2. Inspect Thermostat Wiring
- Turn off power to the HVAC system at the circuit breaker to ensure safety.
- Remove the thermostat cover to access the wiring.
- Check the AUX or W2 terminal for loose or disconnected wires.
- Use a multimeter to test the voltage of the AUX terminal. If no voltage is detected, there may be an issue with the wiring or the thermostat.
3. Test the AUX Heat Components
- Inspect the circuit breakers associated with the AUX heat system. Reset any tripped breakers.
- Check the heat strips for physical damage if your system uses electric resistance heating.
- Test the heating elements for continuity using a multimeter. Replace any damaged components.
4. Inspect the Heat Pump
- Check the outdoor unit for signs of frost or ice. If the heat pump is frozen, manually defrost it by switching to Emergency Heat.
- Verify that the heat pump’s defrost cycle is functioning correctly. A faulty defrost board can prevent AUX heat from activating.
5. Reset or Reprogram the Thermostat
- If the thermostat is not functioning properly, resetting the thermostat sometimes solves the problems.
- Reprogram or recalibrate the thermostat according to the manufacturer’s instructions to ensure accurate operation.
What is AUX Heat and How They Work
“AUX Heat,” which stands for “Auxiliary Heat,” is a backup heating system within a heat pump that automatically turns on when the outdoor temperature drops too low, preventing the heat pump from efficiently reaching the desired temperature on its own; essentially, it provides an extra boost of heat to supplement the heat pump when needed, typically using electric resistance heating elements.
How it works:
- Temperature Trigger
- Your thermostat monitors the outdoor temperature and activates the auxiliary heat when it drops below a certain threshold, usually near freezing temperatures.
- Heat Pump Assistance
- When the auxiliary heat kicks in, it essentially acts as a secondary heating source alongside the heat pump, providing additional warmth to reach the set temperature faster.
- Electric Resistance Heating
- Most auxiliary heat systems use electric resistance heating elements, which directly generate heat through electricity, unlike the heat pump that extracts heat from the air.
Auxiliary heat is meant to be used only when necessary, as it is typically less energy-efficient than the primary heat pump function. Your energy bills may increase when the auxiliary heat is frequently activated due to extremely cold weather. When the auxiliary heat is engaged, you can usually see an “AUX” indicator on your thermostat.
AUX heat automatically activates when:
- The outdoor temperature is too low for the heat pump to extract sufficient heat.
- There’s a significant difference (usually 2-3°F) between the thermostat’s set temperature and the actual room temperature.
When to Call a Professional
If troubleshooting doesn’t resolve the issue, contact an HVAC technician. Professional services may be required to:
- Repair or replace faulty heating elements, defrost boards, or control boards.
- Diagnose and fix electrical issues in the HVAC system.
By following the step-by-step process and understanding the additional information, you can identify and fix AUX heat problems, ensuring your home stays warm and your HVAC system operates efficiently.
