Heat Pump Runs but No Heat: Troubleshooting Common Causes and Fixes

When a heat pump runs but produces no heat, homeowners may face discomfort and uncertainty about repair costs. This article explains the most likely causes—ranging from simple thermostat settings to refrigerant issues—and provides practical steps for diagnosis and resolution. It focuses on safe, effective troubleshooting and when to call a professional.

Symptom	Likely Causes	Simple Actions
Unit runs but blows cool air	Reversing valve fault, thermostat mode, defrost cycle	Check thermostat, listen for defrost, inspect outdoor coil
Airflow but no warmth	Low refrigerant, compressor faults, metering device issue	Look for ice, unusual sounds; call technician for refrigerant
No airflow	Blower motor failure, clogged filter, duct problems	Replace filter, check vents, test fan operation

How Heat Pumps Produce Heat

A heat pump moves heat instead of generating it, extracting warmth from outdoor air or the ground and transferring it indoors through a refrigeration cycle. Key components include the compressor, reversing valve, expansion device, evaporator and condenser coils, and the indoor blower. Proper interaction among these parts is essential for heating performance.

Initial Checks Before Calling A Technician

Several quick checks can identify simple problems that cause a heat pump to run without producing heat. These checks are safe for most homeowners and often resolve issues without a service call.

Verify Thermostat Settings

Ensure the thermostat is set to Heat or Auto with a temperature above room temperature. If a heat pump-specific thermostat has an emergency heat (auxiliary heat) mode, confirm whether it is active; auxiliary heat may be more expensive but will produce warmth when the heat pump is struggling.

Check Air Filters And Vents

A clogged filter or closed vents reduce airflow and heat delivery. Replace filters if dirty and ensure supply and return vents are open and unobstructed. Good airflow is essential for heat transfer and prevents coil freezing.

Inspect Outdoor Unit

Look for ice buildup, heavy debris, or snow around the outdoor unit. Light frost during operation is normal, but heavy ice or thick snow can block heat exchange. Clear loose debris and gently remove snow; do not chip ice on coils.

Common Mechanical And Refrigeration Problems

When basic checks don’t restore heat, the problem may be mechanical or refrigerant-related. These issues typically require a trained technician for safe and accurate repair.

Refrigerant Leaks And Low Charge

Low refrigerant reduces the system’s ability to extract heat from outdoor air. Signs include reduced heating capacity, ice on the outdoor coil, and longer run times with little to no warm air. A technician must locate and repair leaks, then recharge the system to the manufacturer’s specification.

Compressor Failure Or Weak Compressor

The compressor pressurizes refrigerant and drives the heat transfer process. If it fails or runs weakly, the heat pump may run but not heat effectively. Symptoms include unusual noises, tripped circuit breakers, and little temperature rise across the indoor coil. Compressor issues often require replacement or major repair.

Reversing Valve Malfunction

The reversing valve switches the refrigerant flow between heating and cooling modes. If it sticks or fails, the heat pump may operate in the wrong mode and blow cool air while claiming to run in heat. A technician can test the valve and replace or repair it as needed.

Metering Device Problems

The expansion device (capillary tube, TXV, or electronic metering) regulates refrigerant flow. If it malfunctions, the cycle is disrupted and heat exchange becomes inefficient. Indicators include pressure anomalies and fluctuating indoor temperatures. Diagnosing this requires pressure gauges and refrigeration knowledge.

Airflow And Distribution Issues

Even with a properly functioning refrigeration cycle, inadequate airflow or ductwork problems can prevent warm air from reaching living spaces.

Blower Motor Or Fan Problems

If the indoor blower does not run or runs intermittently, warm air won’t circulate. Symptoms include cool returns, hot refrigerant lines but no warm supply air, or the system running without airflow. Motor failure, capacitor problems, or control board issues may be responsible.

Duct Leaks And Poor Insulation

Leaky ducts or poorly insulated runs lose heat before it reaches rooms. Check for disconnected or crushed ducts in attics, basements, and crawlspaces. Seal accessible gaps with mastic or UL-approved foil tape and improve insulation where possible to restore heat delivery.

Electronic Controls And Safety Devices

Modern heat pumps rely on sensors, control boards, and safety switches. Failures in these components can lead to running without heating.

Thermostat Malfunction Or Wiring Faults

A faulty thermostat or loose wiring can send incorrect signals to the heat pump. Verify thermostat batteries, replace if erratic, and inspect wiring terminals for corrosion or loose connections. If uncertain, have a technician test thermostat output and voltages.

Defrost Control And Sensors

Heat pumps enter defrost cycles to clear outdoor coil frost. During defrost, the unit may temporarily produce cool air. If the defrost control or sensors malfunction, the unit may remain in defrost or fail to properly cycle, causing extended periods without heat. Technicians can test defrost sensors and controls for proper operation.

High-Pressure And Low-Pressure Switches

Pressure safety switches protect the compressor. If these switches trip due to abnormal pressures, the unit may run but shut off compressor operation, resulting in no heating. Identifying the root cause—refrigerant restriction, dirty coil, or fan failure—is necessary for repair.

Seasonal And Environmental Factors

Heat pump performance varies with outdoor temperature and humidity. Understanding these limits helps determine whether a system is underperforming or operating normally.

Cold Climate Performance

As outdoor temperatures fall, heat pump efficiency decreases. Many modern cold-climate heat pumps maintain heat at low temperatures, but older units can struggle below 25°F. In extreme cold, auxiliary electric heat or a backup furnace may be necessary to maintain comfortable indoor temperatures.

Defrost And Frost Patterns

Outdoor coils naturally frost in cold, humid weather. Frequent, heavy frosting or prolonged defrost cycles can indicate low airflow, refrigerant issues, or a failing defrost board. Regular inspection during winter months helps identify abnormal patterns early.

When To Call A Professional

Some problems require licensed HVAC technicians due to safety, refrigerant regulations, and specialized tools. Prompt professional service prevents further damage and restores heating quickly.

• Refrigerant Suspected: If refrigeration issues or leaks are suspected, a certified technician must handle repairs and refrigerant recovery.
• Compressor Or Electrical Faults: Complex electrical diagnostics, compressor replacement, or control board repairs need trained personnel.
• Persistent No Heat: After basic homeowner checks, if the heat pump still runs without producing heat, schedule a professional inspection.

Preventive Maintenance To Avoid Future Problems

Regular maintenance extends heat pump life and reduces no-heat events. A seasonal service plan can catch problems before they cause system failure.

Recommended Maintenance Tasks

• Replace or clean air filters every 1–3 months during heavy usage.
• Schedule professional inspections at least once a year, ideally before winter.
• Keep outdoor units clear of debris, vegetation, and snow.
• Seal and insulate ducts annually to maintain airflow efficiency.
• Verify thermostat operation and replace batteries as needed.

Cost Considerations And Expected Repairs

Repair costs vary widely depending on the cause. Simple fixes like filters and thermostat replacements are low cost, while compressor or refrigerant repairs can be expensive. Homeowners should obtain multiple quotes and ensure technicians provide a diagnosis and written estimate.

Issue	Estimated Cost Range (US)
Filter Replacement	$10–$60
Thermostat Replacement	$100–$300
Refrigerant Leak Repair And Recharge	$200–$1,200+
Compressor Replacement	$800–$2,500+
Reversing Valve Replacement	$300–$1,200

Safety Tips And Best Practices

Working around HVAC equipment involves electrical and refrigerant hazards. Homeowners should limit DIY to non-electrical tasks and avoid handling refrigerant. Always turn power off at the breaker before inspecting equipment, and follow manufacturer guidance for safe operation.

Key Takeaways For Troubleshooting A Heat Pump That Runs But Produces No Heat

Check thermostat settings, replace dirty filters, and clear the outdoor unit as first steps. If problems continue, suspect refrigerant issues, reversing valve faults, compressor problems, or airflow restrictions. For refrigerant handling and major mechanical repairs, contact a licensed HVAC technician. Regular maintenance reduces the likelihood of no-heat events and improves system reliability.