Why Your Heat Pump Runs Constantly But Your House Still Feels Cold

A heat pump that never shuts off yet fails to keep the house comfortable is one of the most common efficiency complaints we see in Chattanooga winters. Here are the usual reasons this happens.

1. Undersized unit: If the heat pump was sized for mild weather or an older, less-insulated version of your home, it simply can’t deliver enough heat when outdoor temperatures drop below 35–40 °F. It runs 100 % of the time trying to catch up and still falls short.

2. Low refrigerant charge: A slow leak drops system pressure. The evaporator coil gets too cold, capacity falls, and runtime increases dramatically while delivered heat decreases. You’ll often feel lukewarm air from the vents.

3. Defrost issues: In cold, humid weather the outdoor coil freezes. A normal defrost cycle lasts 5–10 minutes. Faulty defrost boards, sensors, or reversing valves can keep the unit stuck in defrost (or unable to initiate it), so most of its runtime is spent melting ice instead of heating your house.

4. Failing compressor or low superheat/subcooling: A weak compressor can’t raise the refrigerant pressure and temperature enough in heating mode. The system runs continuously at reduced capacity.

5. Extremely dirty outdoor coil: Restricted airflow across the outdoor coil raises head pressure and reduces heat absorption from outside air. The heat pump has to run longer to extract the same amount of heat.

6. Auxiliary heat lock-in (electric strips running full time): If the system thinks the heat pump can’t keep up, it locks on the expensive backup strips. You’ll feel warm air, but the heat pump itself is still running underneath and the power bill skyrockets.

7. Incorrect airflow across the indoor coil: Clogged filters, blocked returns, or a failing blower motor reduce indoor airflow. Delta-T drops, capacity drops, and runtime goes up.

Quick field checks you can do:

• Feel the air from the supply registers — it should be noticeably warmer than body temperature (typically 95–110 °F).

• Look at the outdoor unit in cold weather — heavy ice that never clears is a red flag.

• Check the filter and clean or replace it.

• Listen for the unit reversing into defrost every 30–90 minutes when it’s below 40 °F and humid.

Most of these issues can’t be fixed with a homeowner adjustment. A proper diagnosis requires gauges, thermometers, and checking superheat/subcooling values at current outdoor conditions.

If your heat pump has been running non-stop for days and the house is still chilly, call a technician who actually measures system pressures and temperatures instead of just adding refrigerant or replacing parts by guesswork.

Scenic Air Solutions

East Ridge, TN

423-463-6228

John Giles has been troubleshooting Chattanooga heat pumps for 55+ years, and when you call Scenic Air, you get John and his highly skilled crew. Let us know how we can help!