Your heat pump is running, the fan is blowing, but the air coming out of the vents feels cool or lukewarm — and the house keeps getting colder. It’s one of the most common HVAC complaints in the US, and it can be caused by something as simple as a thermostat setting or as serious as a failing compressor. Below is a complete breakdown of why a heat pump stops heating, what you can safely check yourself, what each repair typically costs in US dollars, and when it’s time to call a NATE-certified technician.
First: Is Your Heat Pump Actually Broken?
Before you panic, understand how a heat pump heats. It doesn’t create heat — it moves it. In heating mode, the outdoor unit absorbs heat from the outside air and moves it indoors through refrigerant.
That means a heat pump delivers cooler supply air than a furnace does:
| System Type | Typical Supply Air Temp | Typical Temperature Rise |
|---|---|---|
| Gas furnace | 120–140°F | 40–70°F |
| Standard heat pump | 85–100°F | 15–30°F |
| Heat pump + aux heat | 95–110°F | 25–40°F |
If your vents feel warm-ish rather than hot, that can be completely normal. The real red flags are: air that’s the same temperature as the room, the outdoor unit not running at all, ice on the outdoor coil, or a system that runs constantly without raising the indoor temperature at all.
Quick Troubleshooting You Can Do Yourself
Work through this checklist before you pick up the phone. Most of these take less than five minutes and cost nothing. For a deeper step-by-step walkthrough, see our full guide to heat pump troubleshooting.
- Confirm the mode. The thermostat should read HEAT, not AUTO or COOL. In Auto, the system may still be responding to a cooling call.
- Set the thermostat 3–5°F above room temperature. A heat pump won’t stage on if the setpoint is within the deadband.
- Check the air filter. A clogged filter starves the system of airflow and can trip the high-limit switch. Replace or clean it every 1–3 months (MERV 8–13 is the sweet spot for most residential systems).
- Check both breakers. There’s a breaker in your main panel and a disconnect box near the outdoor unit. Reset any tripped breaker once.
- Clear the outdoor unit. Remove snow, ice, and leaf debris, and keep 2 feet of clearance on all sides. Never stack snow on top of the cabinet.
- Look at the outdoor unit. Is the fan spinning? Is there frost covering the entire coil? Is the reversing valve solenoid receiving power?
- Check for error codes. Communicating and variable-speed systems (Carrier, Trane, Lennox, Mitsubishi, Bosch) display fault codes on the thermostat or control board. Write the code down — it saves diagnostic time.
The 10 Most Common Causes of a Heat Pump Not Heating
1. Thermostat Settings, Batteries, or Wiring
It’s the least glamorous answer and the most frequent one. A thermostat in Fan Only, a dead battery, a blown 3-amp fuse on the control board, or a miswired O/B reversing valve terminal will all leave you with a running air handler and no heat.
A quick test: switch the thermostat to Emergency Heat (if equipped). If warm air returns, the indoor air handler and aux heat strips are fine and the problem is on the outdoor side. Our thermostat troubleshooting guide covers wiring, calibration, and staging issues in detail.
Typical cost: $150–$500 for a replacement thermostat installed.
2. A Clogged Air Filter or Blocked Return
Restricted airflow is the #1 killer of heat pump efficiency. A dirty filter, a closed return grille, or collapsed flex duct can cause the system to overheat and short-cycle on a limit switch. It also drives up static pressure and can freeze the indoor coil.
3. Tripped Breaker or Failed Disconnect
Heat pumps draw high amperage at startup. A weak breaker, a corroded disconnect, or a loose lug can drop one leg of power. Check the outdoor disconnect for a pulled “fuse block” handle — some installers remove it for service and forget to reinstall it.
4. Failed Capacitor or Contactor
These are the two most common electrical failures in an outdoor unit. A bulging or leaking capacitor prevents the compressor or condenser fan from starting; a pitted contactor prevents the unit from receiving power at all. Both are inexpensive, high-failure-rate parts.
Typical cost: $150–$300 for a capacitor; $150–$350 for a contactor, installed.
5. Defrost Cycle Problems or a Frozen Outdoor Coil
During winter, the outdoor coil collects frost. The defrost control board periodically reverses the system into cooling mode to melt it — usually for 5–15 minutes, during which you’ll see steam and hear a whoosh. Supplemental heat runs during defrost so you don’t feel a draft.
If the board, defrost thermostat, or reversing valve sensor fails, the coil stays iced over and the system can’t absorb heat. A unit that’s a solid block of ice after 30+ minutes is a defrost failure, not a refrigerant problem.
Typical cost: $300–$600 for a defrost board; $200–$450 for a defrost sensor or thermostat.
6. Stuck Reversing Valve
The reversing valve changes refrigerant flow direction between heating and cooling. If the solenoid coil fails or the valve itself sticks, the heat pump stays in cooling mode — which is why “heat pump blowing cold air” and “reversing valve” are so often mentioned together. A gentle tap on the valve body occasionally frees it; usually it needs replacement.
Typical cost: $250–$450 for a solenoid coil; $700–$1,500 for a full reversing valve replacement (it requires recovering refrigerant and brazing).
7. Low Refrigerant Charge or a Leak
A heat pump is a sealed system. If the charge is low, heating capacity drops dramatically and the outdoor coil may frost unevenly. A slow leak — often at a Schrader valve, brazed joint, or coil u-bend — means you need both a leak repair and a recharge.
Note that refrigerant type matters for cost: R-410A systems are being phased down under the AIM Act, and newer equipment uses A2L refrigerants such as R-454B or R-32, which require different handling procedures and, in some cases, different tools.
Typical cost: $250–$800 for leak detection and repair; $400–$1,500+ for a full recharge, depending on refrigerant type and charge size.
8. Compressor Failure
The compressor is the heart of the system and the most expensive component to replace. Symptoms include a humming outdoor unit that never starts, a tripped breaker immediately on startup, or an open winding detected with a multimeter. Systems older than 12–15 years with a failed compressor are usually better replaced than repaired.
Typical cost: $1,200–$2,700 installed. A full heat pump replacement runs $5,500–$12,000+ for a 2–5 ton (24,000–60,000 BTU) system.
9. Auxiliary Heat and Emergency Heat Problems
Heat strips (typically 5–15 kW) and their sequencers, relays, and high-limit switches are a frequent failure point. If the house only heats in EM HEAT, the aux circuit is working and the compressor side isn’t — the reverse of the earlier test. Keep in mind that emergency heat is expensive: a 10 kW strip running continuously can add $10–$20 per day to your electric bill.
10. You’re Below the Balance Point
Every heat pump has a balance point — the outdoor temperature where its capacity exactly matches your home’s heat loss. For standard units that’s usually 30–40°F. Below that, the system leans on aux heat. ENERGY STAR cold-climate certified heat pumps are rated to deliver 100% of nominal heating capacity at 5°F and keep running well below 0°F, but a standard builder-grade unit in a Minnesota January simply won’t keep up without backup.
Also check: is the system oversized or undersized? A 2-ton (24,000 BTU) unit in a 2,800 sq ft home in Climate Zone 5 will run nonstop and never satisfy the thermostat — no repair will fix a sizing problem.
Cost to Repair a Heat Pump That Isn’t Heating
| Repair | Typical Installed Cost (USD) |
|---|---|
| Diagnostic / service call | $75–$200 |
| Air filter (DIY) | $10–$40 |
| Capacitor | $150–$300 |
| Contactor | $150–$350 |
| Defrost control board | $300–$600 |
| Blower motor | $300–$700 |
| Reversing valve | $700–$1,500 |
| Refrigerant leak repair + recharge | $500–$2,000 |
| Compressor | $1,200–$2,700 |
| Full system replacement | $5,500–$12,000+ |
Note: These are national averages. In high-cost metros like San Francisco, Boston, or New York City, expect 25–50% higher labor rates.
Repair or Replace?
Use the $5,000 rule as a rough guide: multiply the equipment’s age by the repair cost. If the result exceeds $5,000, replacement usually wins. A 14-year-old heat pump needing a $1,500 compressor scores 21,000 — replace it. A 6-year-old unit needing a $300 capacitor scores 1,800 — repair it.
Other factors pushing toward replacement:
- Efficiency: Federal minimums now require SEER2 14.3 and HSPF2 7.5 for split systems in most of the US. An older unit running at SEER 10 is costing you real money every month.
- Refrigerant: R-22 systems should be replaced, not repaired — R-22 is no longer produced and costs $100+ per pound.
- Refrigerant detection: New A2L systems require refrigerant detection sensors per UL 60335-2-40, and retrofitting older equipment isn’t practical.
- Incentives: Federal, state, and utility rebates for high-efficiency heat pumps change frequently — check ENERGY STAR and the DSIRE database for current offers in your ZIP code before you commit.
If you’ve narrowed it down to a compressor, reversing valve, or evaporator coil, get a written quote for both repair and replacement from at least two licensed contractors. Our heat pump repair overview explains what a fair estimate should include.
How to Prevent a Repeat Breakdown
- Change filters every 1–3 months. Set a phone reminder. It’s the cheapest maintenance you’ll ever do.
- Schedule bi-annual tune-ups. Spring for cooling, fall for heating. A tune-up runs $100–$250 and typically includes coil cleaning, refrigerant charge verification, electrical inspection, and defrost testing.
- Keep the outdoor unit clear year-round — 2 feet of clearance, no shrubs touching the cabinet, no snow piled on top.
- Don’t use Emergency Heat as a daily setting. It bypasses the compressor entirely and roughly doubles heating costs.
- Watch your electric bill. A sudden 20–30% jump in winter usage without a rate change often signals aux heat running when it shouldn’t.
- Install a smart thermostat with heat pump-specific staging. Generic thermostats misconfigure aux heat lockout and can cost you hundreds per season.
Frequently Asked Questions
Why is my heat pump blowing cold air when I set it to heat?
The most common causes are a thermostat set to Cool, Auto, or Fan Only; a system stuck in defrost mode; a tripped breaker at the outdoor unit; a failed reversing valve; or low refrigerant. If the outdoor unit is running but the air stays cold for more than 15–20 minutes, shut the system off and call a licensed technician.
How much does it cost to fix a heat pump that is not heating?
In the US, a diagnostic visit typically runs $75–$200. Common repairs range from $150–$350 for a capacitor or contactor, $300–$600 for a defrost board, $700–$1,500 for a reversing valve, and $1,200–$2,700 for a compressor. Refrigerant leak repair usually costs $250–$1,500 depending on the location of the leak.
At what outdoor temperature does a heat pump stop working?
A standard heat pump maintains capacity down to its balance point, usually around 30–40°F, and keeps running (with declining output) until about 5–15°F. ENERGY STAR cold-climate certified heat pumps are rated to deliver full heating capacity at 5°F and continue operating well below 0°F. Below the balance point, supplemental electric heat or a dual-fuel furnace takes over.
Conclusion
A heat pump that isn’t heating is rarely a mystery once you know where to look. Start with the free stuff — thermostat mode, filter, breakers, and a clear outdoor unit — then move to the mechanical suspects: capacitor, contactor, defrost board, reversing valve, refrigerant charge, and compressor. Most heating failures fall into a $150–$600 repair range, and only compressor or reversing valve problems approach replacement territory. If you’ve reset the breaker, changed the filter, and confirmed the thermostat is calling for heat and the system still won’t warm the house, stop cycling it — repeated short-cycling can turn a $200 fix into a $2,000 one. Call a NATE-certified technician, have the fault code ready, and get the repair in writing.