Why Is My Heat Pump Not Heating: Common Causes and Fixes

The article explains why a heat pump may not be heating, outlines step-by-step troubleshooting, and offers practical fixes and maintenance tips for homeowners. It targets common search queries like “Why Is My Heat Pump Not Heating” and “heat pump not heating” to provide clear, actionable guidance.

Symptom	Possible Cause	Quick Fix
No Warm Air	Thermostat settings, defrost mode, low refrigerant	Check thermostat, switch to heat, call technician
Weak Airflow	Clogged filter, blocked vents, failing blower	Replace filter, clear vents, inspect blower
Short Cycling	Oversized unit, electrical issue, low refrigerant	Service by pro, check breakers
Outdoor Unit Icing	Defrost failure, low refrigerant	Clear ice, test defrost cycle, call pro

How Heat Pumps Work And Why Heating Can Fail

Heat pumps transfer heat rather than generate it, moving heat from outdoors to indoors using a compressor and refrigerant. They operate efficiently down to moderate outdoor temperatures but rely on components like the compressor, reversing valve, fans, and thermostats. Problems arise when any of these components malfunctions, when airflow is restricted, or when refrigerant is low.

Common Mechanical And Component Causes

Thermostat Misconfiguration Or Failure

Incorrect thermostat settings are a frequent cause of heat pump not heating. The thermostat may be set to “cool”, to the wrong temperature mode, or be on a schedule that prevents heat. A faulty thermostat or incorrect calibration can also stop the system from calling for heat.

Refrigerant Leaks Or Low Refrigerant

Heat pumps require the correct refrigerant charge to transfer heat. Low refrigerant reduces heating capacity and can cause icing on coils. Refrigerant does not vanish without a leak; a certified technician must locate and repair leaks and recharge the system.

Defrost Cycle Problems

In cold or humid conditions, outdoor coils can ice over and the unit periodically enters defrost mode. If defrost controls or sensors fail, the pump may remain in defrost or fail to defrost, reducing heat output. Excessive outdoor unit ice is a red flag.

Compressor Or Reversing Valve Failures

The compressor circulates refrigerant and provides the pressure difference needed for heat transfer. A failing compressor or a stuck reversing valve (which switches between heating and cooling) will impair heating. These issues usually require professional diagnosis and replacement.

Airflow Restrictions: Filters, Ducts, And Vents

Restricted airflow dramatically reduces heating performance. Dirty air filters, blocked vents, closed dampers, or duct leaks can cause weak warm-air delivery and increased system strain. Replacing filters and inspecting ducts often restores normal heating.

Electrical Problems And Safety Switches

Tripped breakers, blown fuses, or faulty contactors can prevent the outdoor unit or compressor from running. Safety devices like float switches in drain pans can shut down equipment if a condensate issue or electrical fault is detected.

Environmental And Installation Factors

Outdoor Temperature Limits

Heat pumps lose efficiency as outdoor temperatures plummet; some units have supplemental electric heat for very cold periods. If the outdoor temperature is below the unit’s effective range and no backup heat is available, perceived failure may be due to operating limits rather than a malfunction.

Improper Sizing Or Poor Installation

An incorrectly sized heat pump (too small for the home) or poor installation (improper refrigerant charge, wrong airflow design) can cause chronic underperformance. Proper load calculation and professional installation are key to consistent heating.

Outdoor Unit Obstructions And Debris

Snow, ice, leaves, or other debris near the outdoor unit can obstruct airflow and heat exchange. The unit needs clear airflow for efficient operation; keeping the area clear helps maintain performance.

Troubleshooting Steps Homeowners Can Take

Check Thermostat Settings And Batteries

Confirm the thermostat is set to Heat or Heat Pump mode, the setpoint is above room temperature, and any schedule or setback features are not blocking heat. Replace thermostat batteries if the display is dim or unresponsive.

Inspect Air Filters, Vents, And Registers

Examine and replace dirty filters. Ensure supply and return vents are open and unobstructed by furniture. Clean registers and vacuum near returns to improve airflow.

Examine The Outdoor Unit

Look for visible ice buildup, blocked coils, or debris around the outdoor unit. If the unit is iced, switch the system to off and gently remove snow or loose ice. Avoid using sharp tools or hot water on coils.

Check Circuit Breakers And Disconnects

Inspect the main electrical panel for tripped breakers or blown fuses for HVAC circuits. Reset a tripped breaker if safe; if it trips again, do not repeatedly reset and call a professional.

Listen For Unusual Noises

Noises like humming, clanking, or grinding from the outdoor unit or indoor air handler suggest mechanical issues like failing motors, loose components, or compressor trouble. Record when noises occur to share with a technician.

Test Auxiliary Heat And Emergency Heat Modes

If the heat pump cannot heat on its own, switching briefly to auxiliary or emergency heat can provide temporary warmth. This confirms the backup heat works but is costlier to operate and not a long-term fix.

When To Call A Professional Technician

Contact a licensed HVAC technician when troubleshooting steps fail, when refrigerant leaks, compressor issues, electrical faults, or reversing valve failures are suspected, or when safety devices have been triggered. Professional service is required for refrigerant handling and complex diagnostics.

Signs That Require Immediate Professional Attention

• Persistent loss of heating after basic checks
• Outdoor unit frozen solid or heavy ice recurring
• Tripped breakers that won’t reset or burning electrical smells
• Hissing sounds indicating refrigerant leaks

Maintenance Practices To Prevent Heat Pump Failure

Regular maintenance extends system life and prevents unexpected failures. Key tasks include replacing filters every 1–3 months, annual professional tune-ups, clearing debris from outdoor units, and verifying thermostat calibration.

Annual Professional Service Checklist

• Refrigerant level check and leak detection
• Electrical connection tightening and component testing
• Coil cleaning and fan motor inspection
• Defrost control operation and reversing valve check
• Airflow and duct leakage assessment

Estimated Repair And Replacement Costs

Costs vary widely by region and issue. Common ranges: simple thermostat replacement $100–$300, refrigerant leak repair and recharge $200–$1,500, compressor replacement $1,000–$3,500, full heat pump replacement $3,500–$10,000 depending on capacity and efficiency. Get multiple quotes and verify contractor licensing.

Energy Efficiency And Alternative Heating Options

If a heat pump struggles in very cold climates, homeowners may consider cold-climate heat pumps designed for lower temperatures or hybrid systems that use heat pumps with gas or electric backup. Upgrading to a higher efficiency model can lower operating costs and improve reliability.

Common Misdiagnoses And Myths

One common myth is that heat pumps produce heat like furnaces; instead, they move heat and their capacity depends on outdoor conditions. Another mistake is repeatedly resetting breakers without addressing the root cause; this can mask electrical faults and risk damage.

Quick Checklist: What To Tell A Technician

1. Describe symptoms (no heat, weak airflow, cycling, icing)
2. When the problem started and any recent events (storms, power outages)
3. Thermostat settings and any recent changes
4. What troubleshooting steps were already taken
5. Any unusual noises, smells, or error codes

Frequently Asked Questions About Heat Pump Heating Problems

Can A Heat Pump Work In Freezing Temperatures?

Yes, many modern heat pumps operate efficiently in cold weather, but performance declines with extreme cold. Cold-climate models maintain higher capacity, and backup heat may be required in prolonged very low temperatures.

Why Does The Outdoor Unit Freeze?

Outdoor unit freezing often indicates a failed defrost cycle, low refrigerant, or restricted airflow. A properly functioning unit should periodically defrost automatically to maintain heating performance.

Is It Normal For A Heat Pump To Cycle On And Off Frequently?

Short cycling is not normal and can indicate oversized equipment, thermostat issues, low refrigerant, or electrical faults. Repeated short cycling shortens equipment life and requires diagnosis.

How Long Should A Heat Pump Last?

With proper maintenance, heat pumps typically last 10–15 years. Lifespan depends on usage patterns, installation quality, maintenance, and local climate.

Resources And Next Steps

Homeowners should consult the heat pump owner’s manual for model-specific guidance and safety instructions. For refrigerant, compressor, electrical, or reversing valve issues, hire an HVAC contractor licensed and insured in the local jurisdiction. Request written estimates and warranties for repairs or replacements.

Key Takeaway: Most heat pump heating issues stem from airflow restrictions, thermostat misconfiguration, refrigerant problems, defrost failures, or electrical faults. Basic checks can resolve some problems, but professional diagnosis is essential for refrigerant or major mechanical failures.