A heat pump that is not heating is a system that runs, hums, and moves air while the vents blow cool or only lukewarm air. It usually shows up on the first cold morning of the year, when the system has sat idle for months, and every weak part is tested at once. Most causes are simple, and a few can be checked in five minutes before you pay for a service call.
This guide lists six causes in the order an HVAC technician checks them, explains when cool air is actually normal, and shows when to call West Air Conditioning for Heat Pump Service.
Why Your Heat Pump Is Not Heating: Let’s Find Out
1. The Thermostat is Set Wrong
Start here, because it costs nothing. A thermostat set to cool, set to off, or set below the room temperature tells a healthy heat pump not to heat, and dead batteries or a blank display do the same. Switch it to heat, raise the target a few degrees above the room temperature, and wait fifteen minutes. If the settings are right and the outdoor unit never starts, the thermostat or its wiring may be at fault, and a technician should test it.
2. The Air Filter is Clogged
A clogged filter restricts the air moving across the indoor coil, so the heat pump delivers less warm air even when every other part works. ENERGY STAR’s maintenance checklist tells owners to inspect, clean, or change filters once a month, and that advice covers heat pumps as well as furnaces and air conditioners. Pull the filter and hold it up to a light. If you cannot see light through it, replace it. A Florida heat pump also cools for most of the year, so its filter has often been working for months before the first cold night.
3. Ice or Frost is Blocking the Outdoor Unit
A coil coated in thick ice cannot pull heat from the outdoor air, so the air indoors turns cool. A little frost is part of normal winter operation. Ice that is still there after the cycle ends is different. Switch the system off at the thermostat, clear leaves and debris from around the unit, and do not chip at the ice, because that can bend the fins or puncture the coil. If ice keeps coming back, a defrost control, a sensor, or a refrigerant problem may be behind it.
4. The Reversing Valve Is Stuck
The reversing valve switches the refrigerant flow between cooling and heating. When it sticks, a heat pump set to heat can keep cooling the house, so the air from the vents stays cool while the outdoor unit runs normally. Confirming this fault takes gauges and a trained technician, and it is one of the pricier repairs. When a repair like that lands on a system more than ten years old, ask for a replacement price alongside the repair quote. West Air Conditioning HVAC Repair and Installation team can price both, so you can compare the two numbers.
5. The System is Low on Refrigerant
Refrigerant is not used up like fuel, so a low level means a leak. A refrigerant leak needs a trained HVAC technician to repair the leak and recharge the system. Typical signs are cool air from the vents, ice on the outdoor coil, a hissing sound, and a system that runs far longer than it used to. Adding refrigerant without fixing the leak only delays the next failure, and handling refrigerant is not a homeowner job.
6. Backup Heat Is Not Working
On cold nights, a heat pump relies on electric heat strips for extra warmth. If a strip fails, a breaker trips, or the thermostat never calls for backup, the house stays cool even though the outdoor unit is running. Check the breaker panel and reset a tripped breaker once. If it trips again, stop and call. Knowing how Aux Heat behaves at each thermostat setting also helps you tell a failed strip from a heat pump that is working as designed.
Is Cool Air From a Heat Pump in Heat Mode Ever Normal?
Yes, cool air is normal for a few minutes when the heat pump runs a defrost cycle, and it is most noticeable when the backup heat is not running. During defrost, the outdoor fan stops, steam may rise from the unit, and the air indoors can feel cooler until the cycle ends. Smell is the other common worry, and it is easier to judge once you know the usual causes. An odor on first start will not last long, so a persistent Burning Smell is the one to treat as a warning, which is why the table below separates dust from danger.
Use this table to tell normal from not normal:
| What You Notice | Normal | Call a Technician |
| Steam from the outdoor unit | Yes, during a defrost cycle | Steam with a burning smell or loud noise |
| Cool air for a few minutes | Yes, during defrost | Cool air that lasts, or returns every cycle |
| Frost on the outdoor coil | A thin film that melts | Thick ice that stays after the cycle ends |
| Dust smell at first start | Yes, and it fades | A burning smell that stays or returns |
If only some rooms stay cool while others are warm, the problem may be Leaking Ductwork instead of the heat pump.
What Can You Check Yourself in Five Minutes?
Work through this list in order and stop when you find the fault:
- Confirm the thermostat is on heat, set above the room temperature, with working batteries.
- Check the air filter and replace it if it is dirty.
- Look at the breaker panel for a tripped heat pump breaker and reset it once.
- Check that the indoor and outdoor power switches are on.
- Look at the outdoor unit, clear loose leaves and debris, and note any ice.
If the house is still cool thirty minutes later, switch the system off and call.
How Much Does a Heat Pump Repair Cost?
Heat pump repair typically costs $150 to $650, averaging $400 nationally, according to Fixr’s 2026 data. Compressor and refrigerant leak repairs cost more, and quotes vary by part and by home. The fault decides the bill, which is why a diagnosis should come first, so a price quoted before anyone looks at the system is a guess. If the system fails at night in a cold snap, emergency HVAC service is available at (407) 739-1667.
Ask for a written quote that separates the diagnostic fee, the part, and the labor, and ask which of the six causes above applied. Bring the make, model, and age of the system if you have them, since they help the technician bring the right parts on the first visit, and keep the quote so you can compare it with a second opinion.
How Can You Stop a Heat Pump From Failing on the First Cold Night?
Test it before you need it. HVAC contractor should check it before each season, and it is suggested to do heating checks in fall because contractors get busy once winter arrives. A pre-winter tune-up in October or November tests the thermostat, filter, electrical connections, heat strips, and the outdoor unit in heat mode, so a weak part is replaced on a mild afternoon, not at midnight. Run the heat for fifteen minutes once before the first cold front and watch for the signs above. Keep a spare filter on hand, clear space around the outdoor unit, and note any odd sounds or smells, so the technician knows where to look when the visit comes.
Final Thoughts
A heat pump that runs without heating usually has a simple cause, from the thermostat mode and a clogged filter to ice, a stuck reversing valve, low refrigerant, or failed backup heat, and the cheapest time to find it is a mild afternoon before the first cold front. If your heat pump runs but the house stays cool, West Air Conditioning can find the fault and give you a clear quote. Request a heat pump repair estimate or call (407) 739-1667 and tell us what you noticed.
Frequently Asked Questions
Why Is My Heat Pump Blowing Cold Air In Heat Mode?
A heat pump blows cool air briefly during defrost, or when the thermostat mode is wrong, the filter is clogged, ice has formed, or refrigerant is low.
How Do I Reset A Heat Pump That Is Not Heating?
Switch the thermostat off, wait a few minutes, then set it to heat. Check the power switches and reset a tripped breaker once. If it trips again, call a technician.
Is It Normal For A Heat Pump To Have Ice On It In Winter?
A thin film of frost is normal, and a defrost cycle clears it, sometimes with steam. Thick ice that stays after the cycle ends needs a technician.
Should I Use Emergency Heat When My Heat Pump Is Not Heating?
Use emergency heat only when the heat pump has stopped working or is frozen, because it relies on backup strips and costs more to run. Then call a technician.
Can A Dirty Air Filter Stop A Heat Pump From Heating?
Yes. A clogged filter restricts airflow across the coil, so the heat pump delivers less warm air. ENERGY STAR advises inspecting, cleaning, or changing filters once a month.