October 31, 2026
Heat Pump Not Heating? Defrost Mode, Common Causes and Fixes for Los Angeles Homes
Short answer: If your heat pump is not heating well, first make sure the thermostat is set to Heat (not Emergency or Cool), replace a dirty air filter, and check that the outdoor unit is clear of debris. Brief cool air and steam from the outdoor unit can be normal defrost mode. If it blows cool air for long stretches, runs constantly without warming the home or makes unusual noises, call a licensed technician.
How a heat pump heats your home
A heat pump moves heat instead of burning fuel. In winter it pulls heat from outdoor air and delivers it indoors; in summer it reverses and works like an air conditioner. Because Los Angeles winters are mild, heat pumps are a popular and efficient option. If you are comparing systems, see heat pump vs gas furnace in California.
What is defrost mode?
When the outdoor coil gets cold and damp, frost can form on it. The heat pump periodically runs a defrost cycle to melt it. During defrost you may notice:
- Steam or vapor rising from the outdoor unit
- The outdoor fan stopping for a few minutes
- Slightly cooler air from the vents for a short time
- Water dripping from the outdoor unit
This is normal and usually lasts a few minutes. It is a concern if the unit stays frozen, ice builds up thickly, or the defrost cycle runs constantly.
Common reasons a heat pump is not heating
| Symptom | Possible cause | What to do |
|---|---|---|
| Blows cool air, thermostat on Cool | Wrong mode | Switch to Heat |
| Weak airflow | Dirty filter, blocked vents | Replace filter, open vents |
| Heavy ice on the outdoor unit | Defrost problem, airflow or sensor issue | Turn off and call a technician |
| Runs nonstop, home stays cool | Low refrigerant, failing reversing valve or compressor, undersized system | Call a technician |
| Outdoor unit will not start | Tripped breaker, failed capacitor or contactor | Check breaker once; call a technician if it persists |
| Heat strips or auxiliary heat running a lot | Heat pump struggling; may raise electric bills | Schedule an inspection |
What to check first
- Thermostat: set to Heat, with the temperature above room temperature. Avoid leaving it on Emergency or Auxiliary heat unless instructed.
- Air filter: replace if dirty.
- Vents and returns: make sure they are open and unobstructed.
- Outdoor unit: clear leaves, debris and anything stacked around it. Do not chip ice.
- Breaker: reset a tripped breaker once. If it trips again, stop.
- Give it time: heat pumps deliver warm, not hot, air, and a stable temperature rather than short blasts.
If you are unsure how your thermostat is configured, a smart thermostat can make settings and error alerts clearer.
When it is time to call a pro
- The outdoor unit is heavily iced or stuck in defrost
- Air stays cool for long periods in Heat mode
- You hear grinding, banging or loud buzzing
- Your electric bill spikes with no change in usage
- The system is older and failing repeatedly
Heat pumps are serviced like air conditioners, with the added reversing valve and defrost controls. See our tune-up cost guide and consider a TOP CLUB maintenance plan to catch problems early. For a gas furnace instead, use our furnace troubleshooting guide.
Repair or replace?
A heat pump that is 12 to 15 years old with a major failure may be a candidate for replacement. Newer models are more efficient and may qualify for rebates; check 2026 AC and heat pump rebates by utility and read heat pump installation in Los Angeles: costs and rebates. If an older home needs more electrical capacity, see whether you need a panel upgrade.
Frequently asked questions
Is steam from my heat pump normal?
Yes, during defrost. It should stop within minutes. If the unit stays iced over, call a technician.
Why does my heat pump blow cool air in winter?
It may be in defrost mode, set to the wrong mode, or have a problem such as low refrigerant. Heat pump air also feels cooler than furnace air even when working properly.
Should I use emergency heat?
Only if instructed or if the heat pump has failed, since it typically uses more electricity.
Do heat pumps work in Los Angeles winters?
Yes. Our mild climate is well suited to them.
Can a heat pump freeze up?
The outdoor coil can frost lightly and defrost on its own. Thick or persistent ice means something is wrong.
Heat pump service in Canoga Park and nearby
TOP AC installs and repairs heat pumps, including Mitsubishi Electric systems, with a 12-year warranty on qualifying systems. See heat pump installation in Canoga Park, heater repair and heating repair in Canoga Park, or explore Woodland Hills, Northridge, Studio City, Thousand Oaks and more.
Heat pump not keeping up? Request service or call (855) 999-8672, 24/7. TOP AC Inc., 21201 Victory Blvd, Suite 102, Canoga Park, Los Angeles, CA 91303 · CSLB #959168.