Heat Pump Not Heating / Blowing Cold Air

By HVAC Load Calculate Team, licensed HVAC professionals · Updated July 2026

The most likely cause is reversing valve stuck in cooling mode, or outdoor temperature below heat pump range. Heat pump runs but only blows cold air in heating mode, fails to produce warm air, or stays in cooling mode. Most cases take diy troubleshooting: 45 min | professional diagnosis: 1-2 hours | reversing valve replacement: 3-5 hours to resolve once you know which cause you are dealing with, and the checks below start with the ones you can do yourself in a few minutes.

How to Confirm This Is Your Problem

You are probably dealing with this exact issue if you notice one or more of these signs:

Heat pump runs but air feels cold
Outdoor fan runs but no heat inside
Thermostat shows heating mode but produces cold air
Auxiliary heat never kicks on
Slight cool breeze from vents instead of heat
Heat pump sounds normal but no warmth
Emergency heat works but normal heat doesn't
Worked fine in cooling, fails in heating
Indoor unit runs constantly with no heat output
Outdoor unit runs but produces no heat transfer

Step-by-Step Diagnosis

Follow these steps to identify the exact cause of your problem:

Verify thermostat is set to Heat mode, not Cool
Check thermostat temperature set 5 degrees above room temp
Confirm heat pump is not in emergency heat mode
Listen for reversing valve click when switching from cool to heat
Feel air from vents - should be lukewarm at minimum (90-100°F)
Check if outdoor unit is running and fan spinning
Inspect outdoor unit for heavy ice or frost buildup
Verify both indoor and outdoor units are powered on
Check if auxiliary heat indicator appears on thermostat
Note outdoor temperature - below 25°F affects efficiency
Test cooling mode to see if compressor works
Check refrigerant lines for temperature difference between supply/return

What Causes It, Ranked by Likelihood

1. Reversing valve stuck in cooling mode

If the system blows cold air on a heat call in winter, the reversing valve may be stuck on the cooling side. Confirmation and repair need a tech with gauges; the valve or its solenoid runs $500 to $1,500.

One of the most frequent culprits. This one needs a professional, typical cost $400-1,200 (professional).

2. Defrost mode stuck on

Defrost temporarily runs the system in cooling to warm the outdoor coil, normally for 5 to 10 minutes. Stuck there, you get continuous cool air indoors and steam off the outdoor unit. A failed defrost board or sensor is the usual cause.

Worth checking after the common causes. This one needs a professional, typical cost $200-600 (defrost control).

3. Low refrigerant charge

Low charge hits heating harder than cooling. Supply air only 5 to 10 degrees above room temperature instead of the normal 15 to 25 means weak capacity, and low charge leads the suspect list. Tech visit required.

Worth checking after the common causes. This one needs a professional, typical cost $500-1,500 (leak repair + recharge).

4. Failed auxiliary heat strips

The strips carry the house below the heat pump balance point. When they fail, the heat pump alone cannot keep up on cold nights even though it runs fine in mild weather. A tech checks the sequencer and elements; repairs run $200 to $600.

Worth checking after the common causes. This one needs a professional, typical cost $300-800 (heat strip replacement).

5. Outdoor temperature below heat pump range

Standard heat pumps lose most capacity below about 25 degrees, and older units below 30. If the house holds fine at 40 out but loses ground at 20, the equipment may just be at its design limit, and the strips should be covering the gap. If they are not, see auxiliary heat.

One of the most frequent culprits. This one needs a professional, typical cost $0 (use emergency heat).

6. Frozen outdoor coil blocking heat transfer

An iced coil cannot absorb heat from outdoor air. If ice persists past a defrost cycle or two, stop running the unit and address the defrost system before something bends.

Worth checking after the common causes. You can usually fix this yourself, typical cost $0-100 (DIY defrost).

7. Failed reversing valve solenoid

The solenoid coil that shifts the valve costs far less than the valve itself, $150 to $350 installed. A tech checks the coil for continuity before condemning the valve; make sure yours does.

Less common, but it happens. This one needs a professional, typical cost $150-400 (solenoid replacement).

8. Thermostat configured for AC only

Heat pump thermostats need the correct system type and O/B wire setting. After a thermostat swap, a wrong configuration gives you cooling but no heating, or backwards operation. Recheck the installer settings menu before paying for a service call.

Less common, but it happens. You can usually fix this yourself, typical cost $0 (reconfigure).

9. Dirty indoor coil reducing heat transfer

In heating mode the indoor coil releases the heat. Coated in dust, it cannot, so the compressor works harder for less output. Coil cleaning runs $150 to $400 and often restores 10 to 20 percent of lost capacity.

Worth checking after the common causes. This one needs a professional, typical cost $100-300 (coil cleaning).

DIY Solutions

You will need replacement air filter, shovel (for snow removal), flashlight, thermometer (to check vent temperature). Plan on 30-45 minutes + 2-4 hours defrost time.

Verify thermostat heat pump settings are enabled (not AC-only mode)
Switch thermostat to cooling mode briefly, then back to heating
Listen for reversing valve "click" sound when switching modes
Check outdoor temperature - if below 25°F, use emergency heat temporarily
Inspect outdoor unit for ice buildup blocking coils
Turn off heat pump if outdoor unit is heavily iced
Allow 2-4 hours for complete defrosting of outdoor unit
Clear snow and debris from around outdoor unit
Replace air filter to ensure proper airflow
Test auxiliary heat by switching thermostat to emergency heat
If emergency heat works, reversing valve likely failed
Check that outdoor unit has adequate clearance (2 feet all sides)
Verify both circuit breakers are on for indoor and outdoor units
After defrost, switch back to normal heat and monitor
If still blowing cold, call professional for reversing valve diagnosis

Before you start, know these safety limits:

Never pour hot water on frozen outdoor unit - causes thermal shock damage
Do not run heat pump with heavily iced outdoor unit - damages compressor
Emergency heat uses expensive resistance heating - only for temporary use
Turn off power before clearing debris from outdoor unit

When to Call a Professional

Stop and call a licensed technician if you run into any of these situations:

No click from reversing valve when switching modes
Heat pump works perfectly in cooling but not heating
Emergency heat works but normal heat doesn't
Refrigerant lines show oil stains indicating leak
Ice reforms on outdoor unit repeatedly after defrost
Loud grinding or clicking from outdoor unit
Heat pump older than 10 years with sudden heating failure
Outdoor unit runs but feels cold to touch in heating mode
Auxiliary heat never activates despite cold temperatures
Recent refrigerant smell near outdoor unit

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How to Keep It From Happening Again

Schedule professional maintenance twice yearly (spring and fall)
Keep outdoor unit elevated above snow level in winter
Clear snow and ice from outdoor unit within 12 hours
Replace air filters monthly during heating season
Install programmable thermostat with heat pump-specific settings
Test heating mode before cold weather arrives
Ensure outdoor unit has 2-foot clearance from shrubs and structures
Upgrade to cold climate heat pump if temperatures regularly drop below 15°F
Install backup heat source for extreme cold events
Monitor defrost cycles - should occur every 30-90 minutes in cold weather

Frequently Asked Questions

Why does my heat pump blow cold air in winter?

Heat pumps blow cold air in winter when the reversing valve is stuck in cooling mode, refrigerant is low, outdoor coils are frozen, or the defrost cycle malfunctions. Heat pumps also blow cool air during normal 5-10 minute defrost cycles. If cold air persists beyond defrost cycles, the reversing valve likely failed.

At what temperature do heat pumps stop heating effectively?

Standard heat pumps lose efficiency below 40°F and struggle below 25-30°F. Cold climate heat pumps work effectively down to -15°F. Below these thresholds, auxiliary heat should automatically activate. If your heat pump blows cold air above 40°F, it has a mechanical problem, not a temperature limitation.

How can I tell if my heat pump reversing valve is bad?

A bad reversing valve causes heat pumps to work in one mode but not the other. Test by switching from heat to cool - you should hear a distinct "click" from the outdoor unit. No click means valve failure. Heat pumps stuck in cooling mode while set to heat indicate a stuck reversing valve.