Auxiliary heat normally runs during defrost, on very cold nights, and when you raise the thermostat several degrees at once. It should not run most of the day in mild weather. Constant aux heat usually points to thermostat configuration, a failed outdoor sensor, low refrigerant, or an undersized heat pump, and it can sharply raise electric bills.
Technical Consideration
Aux heat: normal or not?
| Situation | Normal? |
|---|---|
| During a defrost cycle (a few minutes) | Yes |
| After raising the setpoint 3+ degrees | Often |
| Below the balance point on a cold night | Yes |
| All day at 40°F outdoors | No: request diagnosis |
| Emergency heat selected on thermostat | No: switch back to Heat |
What is the difference between aux heat and emergency heat?
Aux heat supplements the heat pump automatically; emergency heat turns the heat pump off and uses backup heat only.
Emergency heat is for when the outdoor unit has failed, not for cold days.
Which thermostat settings matter?
Aux heat lockout temperature, compressor lockout, droop or differential, and adaptive recovery all control when strips turn on.
Smart thermostats installed without heat pump settings are a common cause of constant aux heat.
How do setbacks affect aux heat?
Large overnight setbacks force aux heat in the morning to catch up.
Smaller setbacks, or none, often cost less with a heat pump.
When is it a mechanical problem?
Low refrigerant, a stuck reversing valve, a failed defrost board, or an iced coil all reduce heat pump output and bring on aux heat.
If settings are right and aux still runs constantly, request diagnosis.
Related services in Wilmington
- Heat Pump Repair in Wilmington, DE
- Smart Thermostats, Zoning & Controls in Wilmington, DE
- Heat Pump Installation in Wilmington, DE
Local verification resources
Before authorizing work, use the Delaware license lookup. For projects that may require approval, consult the City of Wilmington permit information or the authority serving the property.