Heat Pump Not Heating or Cooling? Troubleshooting Guide for Frozen Units, Cold Air, Short Cycling, and Common Heat Pump Problems
November 9, 2026
A heat pump that blows cold air or ices over is often less broken than it looks. Some of it is designed behavior, like a defrost cycle. Most real problems start at the thermostat, a breaker, the filter, or the outdoor unit. This guide shows which symptoms are normal and where your part of the fix ends. We make air filters at Filterbuy, so we read every heat pump problem through airflow first, and we say plainly when the fix is past a filter.
TL;DR
Heat pump not heating or cooling? Check the thermostat, both breakers, the air filter, and the outdoor unit. Cool air for up to 15 minutes during defrost is normal. Call a technician for ice that will not clear, grinding, a breaker that trips twice, or persistent short cycling.
Key Takeaways
Heat pump air runs near 105°F versus about 130°F from a furnace.
Defrost cycles of 5 to 15 minutes, with steam, are normal.
If heating and cooling both fail, check shared parts first: power, thermostat, blower, and filter.
A clogged or loose filter can cause icing and short cycling.
Refrigerant work requires an EPA Section 608 certified technician.
Heat Pump Not Working? Match Your Symptom to the Likely Cause
Find your symptom, rule out the normal explanation, then read its section below. The last column marks when to call a pro.
Table 1: Heat Pump Symptoms, Normal vs. Call a Pro
Defrost timing per Efficiency Works. Restart delays vary by model.
A Heat Pump Troubleshooting Shortcut: The Two-Mode Test
A heat pump heats and cools with one refrigerant circuit, so the failing mode narrows the cause. On a mild day, run each mode for a few minutes. Many manufacturers advise against cooling in cold weather, so check your owner's manual first.
Table 2: Filterbuy's Two-Mode Test, Heating vs. Cooling
Run cooling only on a mild day.
Why Is My Heat Pump Not Heating or Blowing Cold Air?
Cold air is often a defrost cycle or heat milder than a furnace's. Efficiency Works, a Colorado utility program, puts heat pump air near 105°F and furnace air near 130°F.
Set the thermostat to Heat, a few degrees above room temperature, with the fan on Auto. The U.S. Department of Energy notes continuous fan operation can reduce heat pump performance unless the motor is variable-speed.
Use Filterbuy's 15-minute rule. Time the cool air. If it stops within about 15 minutes, with a paused outdoor fan and steam outside, that was defrost. If it keeps going, it is a fault.
Avoid deep setbacks, which can trigger backup electric heat that DOE says usually costs more.
Hold the filter to a light. If little light passes through, replace it.
If cool air continues or the outdoor unit is not running, suspect the reversing valve, defrost control, or refrigerant, all technician repairs.
Why Is My Heat Pump Not Cooling?
If the house stays warm, start with airflow. Set the thermostat to Cool below room temperature and replace a dirty filter. Outside, confirm the fan spins and clear 24 inches around the unit. DOE advises cleaning a dirty coil with fan power off.
Summer ice on the lines, hissing, or warm air while the outdoor unit runs points to low refrigerant. Turn cooling off and schedule service.
Heat Pump Frozen: Normal Frost or a Real Freeze-Up?
Thin frost that melts during defrost is normal. A coil encased in ice, or ice on the indoor unit, is not. Never chip at ice, because coil fins puncture easily. Steam or smoke? Steam thins out within a few feet and has no odor. Smoke lingers and smells, so shut the system off.
Check for roof drip onto the outdoor unit and clear snow from its sides.
Replace a clogged filter and open closed returns. The DOE-funded Building America Solution Center notes excessive filter pressure drop can freeze coils.
If ice stays after a full defrost cycle, switch to emergency heat and call a technician.
For the indoor side of the problem, see Filterbuy's guide on why a heat pump filter can freeze, and run our heat pump winter prep checklist before the next cold snap.
Why Is My Heat Pump Running Constantly or Short Cycling?
Long runs are normal in cold weather, since heat pumps are designed to run longer. Heat pump short cycling, on and off every few minutes, never is.
Constant running is a problem when the house never reaches the setpoint. Look for a clogged filter, closed vents, a dirty coil, or low refrigerant. Short cycling usually traces to a restricted filter, a thermostat near a heat source, or an oversized system. If it continues after a new filter, call a pro.
Why Is My Heat Pump Making Noise?
A brief whoosh or click as defrost starts or ends is the reversing valve shifting, and it is normal.
Rattling: often a loose panel or debris in the fan.
Banging at startup from the return: replace a filter that bangs when the system starts.
Grinding or squealing: likely motor bearings. Shut it off.
Buzzing or humming without starting: often a capacitor or contactor, a job for a pro.
Why Is My Heat Pump Not Turning On?
A heat pump that will not start usually has a power or control problem. Replace dead thermostat batteries. Reset a tripped breaker once. Confirm the outdoor disconnect is in place. Many systems also have a condensate switch that shuts down when the drain clogs.
If a breaker trips again or you smell burning, one of the electrical warning signs ESFi lists, leave it off and call a technician.
When to Stop and Call a Licensed Technician
Call a pro for refrigerant, electrical parts, the compressor, the reversing valve, or defrost controls. Ask for a NATE-certified technician, and hand over a five-line note:
Which mode fails: heat, cool, or both.
The outdoor temperature when it started.
Whether the outdoor fan and compressor run.
Where ice sits: outdoor coil, indoor unit, or lines.
Which symptom came first, and your last filter change.
Filterbuy's DIY versus professional repair guide covers safety steps. Compare heat pump repair costs and the repair-or-replace math, and watch for early warning signs your heat pump needs repair. In cold climates, see our guide to the NEEP cold-climate list and whether heat pumps work in cold climates. In South Florida, a Filterbuy HVAC Solutions maintenance care plan schedules yearly service.
What Making Filters Taught Us About Heat Pump Problems
We build filters to order, which shows us airflow problems a thermostat never reports. Three lessons:
A clean-looking filter can still be the problem. A filter that flexes or sits loose lets air slip around the edge. The media looks clean because dust went around it, toward the coil.
Order by the size printed on the frame. We cut filters slightly under nominal so they seat. A Filterbuy 20x25x1 measures 19.5 x 24.5 x 0.75 inches, so measuring the slot can lead to the wrong order.
More MERV is not automatically better. Check your HVAC manual first, since denser media adds airflow resistance.
Filterbuy builds pleated heat pump replacement air filters in MERV 8, 11, and 13, in more than 600 sizes plus custom sizes. MERV 11 air filters suit most homes. Our heat pump filter guide covers fit, and Filterbuy auto-delivery handles timing.
"The question I get asked most is which MERV number is best. It is the wrong question. The best filter is the highest rating your system can move air through, in the deepest size your cabinet will take, changed on time. We make every rating on that scale, so I have no reason to sell you a number."
Michelle Wan, Brand Manager and Air Quality Writer, Filterbuy
Essential Resources
ENERGY STAR Maintenance Checklist: tune-up checklist.
EPA Section 608 Technician Certification: refrigerant service rules.
Building America Solution Center: High-MERV Filters: filter pressure drop.
NEEP ccASHP Specification and Product List: cold-climate heat pumps.
Why Choose a NATE-Certified Technician: hiring certified techs.
Manual J Calculations: What and Why?: oversizing and short cycling.
Understanding Your Heat Pump: defrost and run times.
Final Thoughts
Check power and the filter first, then hand the rest to a technician.
Next Steps
Match your symptom in Table 1.
Set a filter reminder or auto-delivery.
Book a yearly tune-up and bring Filterbuy's heat pump maintenance checklist.
"In the field, the filter rarely gets blamed for the thing it actually caused. A frozen coil or a blower running long gets written up as a refrigerant or thermostat problem, when the real cause was a loaded filter nobody changed. Before paying for a diagnosis, pull the filter and hold it up to a light."
David Clark, Licensed HVAC Technician
Supporting Statistics
About 30% more energy use from installation faults.
NIST tested faults like low airflow and wrong refrigerant charge.
Most systems checked in the field ran below rated efficiency.
Why it matters: these faults also cause short cycling and icing.
Source: Underperforming? Energy Efficiency of HVAC Equipment Suffers Due to Poor Installation
13% of U.S. homes, but 41% in South Carolina.
Share of homes heating mainly with a central heat pump, 2020.
North Carolina reached 38% and Florida 31%.
Why it matters: a failure leaves many Southern homes without main heat.
Source: Highlights for Space Heating in U.S. Homes by State, 2020
Heat pumps outsold gas furnaces in 2025.
About 3.64 million heat pumps shipped.
About 3.25 million gas furnaces shipped.
Why it matters: more owners are troubleshooting one for the first time.
Source: AHRI Monthly Shipments
Frequently Asked Questions
Why Is My Heat Pump Blowing Cold Air in Heat Mode?
Usually a defrost cycle or a fan set to On. Cool air past 15 minutes suggests a fault.
How Long Should a Heat Pump Defrost Cycle Last?
Typically 5 to 15 minutes, several times a day in cold, damp weather.
Should I Use Emergency Heat When My Heat Pump Stops Heating?
Only as a stopgap until a technician arrives, because backup electric heat usually costs more. AUX on the thermostat is different: it turns on automatically during defrost or deep cold, which is normal. EM heat is the manual switch that bypasses the heat pump.
Can a Dirty Air Filter Cause a Heat Pump to Freeze Up?
Yes. A clogged filter reduces airflow across the coil, which can lead to icing and short cycling.
How Do I Reset a Heat Pump?
Turn the thermostat off, switch off both breakers, wait about five minutes, then restore power.
Start With the Filter
Shop Filterbuy air filters by size in MERV 8, 11, or 13, with fast and free 2-day delivery to most US states.
Glossary
Defrost cycle: a brief reversal that melts frost on the outdoor coil.
Reversing valve: switches a heat pump between heating and cooling.
Short cycling: turning on and off every few minutes.
MERV: Minimum Efficiency Reporting Value, the 1 to 16 filter efficiency scale.