Why Your Heat Pump Keeps Running: Causes, Fixes, and When to Call

If a heat pump runs all the time, it may be completely normal—or a sign of trouble. This guide explains why a heat pump keeps running in cold or hot weather, how to spot issues, and what to do next. It covers thermostat settings, defrost cycles, refrigerant problems, airflow, insulation, and when to call a professional. Actionable checklists and cost ranges help prioritize fixes.

What Normal Heat Pump Operation Looks Like

Unlike gas furnaces that cycle on and off, heat pumps often run for longer, gentler cycles. This steady operation is by design, delivering efficient comfort and stable humidity. In cold snaps or heat waves, longer runtimes are expected.

Variable-speed and two-stage systems may run continuously at low speed to maintain set temperature efficiently. That’s usually normal, quiet, and cost-effective. However, if a single-stage unit runs nonstop and struggles to meet setpoint, there may be a problem.

In winter, heat pumps periodically defrost the outdoor coil. During defrost, the fan may stop and steam may appear. That’s normal and brief. Defrost cycles lasting minutes and occurring every 30–90 minutes in freezing, humid weather can be typical.

Why Does My Heat Pump Keep Running In Heating Mode?

Cold Weather And The Balance Point

Every home and system has a “balance point”—the outdoor temperature where the heat pump’s output equals the home’s heat loss. Below that temperature, the unit runs longer and may need auxiliary heat to keep up. Older systems often balance near 35–40°F. Modern cold-climate, variable-speed models can heat efficiently into the teens or lower.

If temperatures plunge well below your system’s capability, continuous running can be normal. Look for signs of strain: large temperature swings, rising energy bills, or rooms that never reach setpoint. Those suggest undersizing, airflow issues, or mechanical faults.

Auxiliary Or Emergency Heat Running Too Often

Electric resistance heat strips provide backup heat when the heat pump alone can’t maintain temperature. If AUX HEAT appears frequently or for long periods, energy use can spike and runtime will be long. Causes include extreme weather, a tight thermostat differential, a failing outdoor unit, or low refrigerant.

Ensure the thermostat is not set to Emergency Heat unless the outdoor unit is down. Emergency bypasses the heat pump and forces expensive electric heat. Use only when the heat pump is inoperable and call a technician promptly.

Thermostat Settings And Fan Mode

Overly narrow temperature differentials or high cycles-per-hour can keep the system running. For heat pumps, a setting of 2–3 cycles per hour is typical. Some smart thermostats have adaptive recovery that preheats slowly. That can look like longer runtime but improves comfort and efficiency.

Set the fan to AUTO, not ON. Fan ON runs the blower continuously, blowing room-temperature air between cycles. That can make it feel like the heat pump never stops, and it may worsen humidity control.

Dirty Filter Or Coils Restricting Airflow

Clogged filters and dirty indoor or outdoor coils reduce heat transfer. The heat pump runs longer but delivers less heat. Replace or clean filters every 1–3 months. Clean outdoor fins gently with a hose when the unit is off. Keep 2–3 feet of clearance around the outdoor cabinet.

At the air handler, a dirty evaporator coil can cause icing, low airflow, and long runtimes. If you suspect coil issues, call a pro for safe cleaning. Avoid chemical sprays without guidance; many can harm fins or coatings.

Low Refrigerant Or A Refrigerant Leak

Low charge reduces capacity and efficiency, forcing long runtimes. Signs include poor heating, icing on the outdoor unit beyond normal frost, hissing sounds, and fluctuating pressures. Heat pumps typically use R‑410A; newer models may use R‑454B or R‑32.

Refrigerant does not “get used up.” If charge is low, a leak exists. A licensed technician should find and fix the leak, then weigh in the correct charge. Topping off without repair is a short-term, costly bandage.

Outdoor Unit Blocked By Debris, Snow, Or Ice

Leaves, grass clippings, or snow drift can choke airflow. After storms, clear snow away from the cabinet and the base pad. In heavy freezing rain, a solid ice shell can form. Do not chip ice with tools. Switch to Emergency Heat temporarily and allow the unit to thaw, or use warm water gently if safe.

Ensure downspouts do not dump water onto the unit, which can refreeze. A simple diverter or a small shelter that maintains clear top and side airflow can help in icy climates.

Frequent Or Long Defrost Cycles

Frost on the outdoor coil is normal near 20–40°F in humid air. The system periodically reverses to cooling mode to melt frost, then shifts back. If defrost is too frequent or lasts unusually long, a failing defrost sensor, control board, or poor airflow may be to blame.

Check the outdoor coil and fan for debris and the sensor probe for secure placement (a pro task). Excess frost after a defrost cycle suggests low refrigerant or a stuck reversing valve.

Undersized Or Aging System

A heat pump that is too small for the home or has lost capacity over time will run continuously in cold weather. Signs include acceptable performance on mild days but poor performance during cold snaps. If the system is 12–15 years old, efficiency and capacity may have declined.

A Manual J load calculation can confirm sizing. Upgrading to a higher HSPF2, variable-speed heat pump or adding targeted insulation and air sealing often fixes chronic runtime issues.

Duct Leaks, Closed Vents, Or Airflow Imbalances

Leaky ducts can dump heated air into garages, attics, or crawlspaces. The heat pump runs longer to compensate. Closed supply registers can raise static pressure and reduce total airflow, hurting coil performance and comfort.

Have a pro measure static pressure and test for duct leakage. Sealing ducts and balancing airflow can cut runtime and bills. In many U.S. homes, duct leakage exceeds 20%, which is significant.

Electrical Or Control Failures

Stuck contactors, failed sensors, bad capacitors, weak blower motors, or a reversing valve issue can keep a heat pump running inefficiently. Symptoms might include outdoor fan not spinning, short defrosts, humming without proper heating, or tripped breakers.

These are pro-level diagnostics. Do not bypass safeties or repeatedly reset breakers. Document error codes from the thermostat or control board to help the technician.

Poor Home Insulation And Air Leaks

Even a perfect heat pump can run constantly if the house leaks heat. Attic insulation below current recommendations, unsealed recessed lights, leaky attic hatches, and drafty windows increase runtime. Air sealing and targeted insulation often deliver faster comfort improvements than equipment changes.

Weatherstrip doors, seal obvious gaps with caulk or foam, and consider an energy audit with a blower-door test to locate major leaks.

Why A Heat Pump Keeps Running In Cooling Mode

Extreme Heat, Solar Gain, And Humidity

In heat waves, a properly sized heat pump may run continuously during peak afternoon hours. Large west-facing windows, poor shading, and high humidity increase cooling load. A heat pump also dehumidifies, and in muggy climates it may run longer to wring out moisture.

Use shades, awnings, or reflective films on sun-exposed windows. Keep the setpoint realistic—dropping from 78°F to 68°F on a 100°F day may be unrealistic and force nonstop operation.

Dirty Condenser, Filter, Or Low Refrigerant

A dirty outdoor condenser coil severely reduces cooling capacity. Clean fins gently with water and a soft brush. Replace dirty filters. If cooling is weak despite clean coils and filters, low refrigerant or a metering device problem may be involved. That warrants professional service.

Thermostat Differential Too Tight

If the cooling differential is set extremely tight, the system may run nearly nonstop to hold a precise temperature, especially with indoor heat gains from cooking, electronics, or guests. A 1–2°F differential typically balances comfort and runtime.

Duct Leaks And Attic Heat

Leaky attic ducts pull in superheated air, reducing supply temperature and forcing long runtimes. Insulate and seal ducts in attics and crawlspaces. Ensure attic ventilation and insulation are adequate to reduce heat infiltration into living spaces.

Quick DIY Checklist Before Calling A Pro

• Check the thermostat: Set to HEAT or COOL as needed, fan set to AUTO, not ON. Confirm no Emergency Heat unless required.
• Adjust setpoints: Use moderate changes. In winter, the DOE suggests 68°F when occupied; in summer, 78°F with fans can feel cooler.
• Replace the filter: If it looks dirty, replace it. Ensure correct size and MERV rating compatible with your system.
• Inspect outdoor unit: Clear debris, leaves, and snow within 2–3 feet. Ensure the fan spins freely when operating.
• Look for ice: Light frost is normal. A solid ice block is not—switch to Emergency Heat and call a pro.
• Check vents: Open supply registers. Do not block with furniture. Verify strong airflow in multiple rooms.
• Listen and observe: Note unusual noises, short cycling, or error codes. Photos and notes help technicians.
• Verify breakers: If tripped, reset once. If it trips again, stop and call for service. Frequent trips indicate electrical issues.

Symptom-to-Solution Guide

When To Call A Licensed HVAC Technician

Call a pro if the heat pump runs constantly yet cannot reach setpoint, the AUX light stays on above freezing, the outdoor unit ices over solid, breakers trip repeatedly, or you suspect a refrigerant leak. Safety-critical and sealed-system work require EPA-certified technicians.

What Diagnostics They Perform

• Static pressure and airflow checks to verify proper duct performance and blower operation.
• Refrigerant charge verification using manufacturer-specified subcooling/superheat and ambient conditions.
• Electrical tests on contactors, capacitors, motors, relays, and control boards.
• Defrost system sensor and board testing; thermostat wiring and settings review.
• Leak detection using electronic sniffers or UV dye, then repair and recharge by weight.
• Load evaluation and equipment sizing review if runtime issues persist in design conditions.

Typical U.S. Repair And Service Costs

Prices vary by region and brand. These ballpark ranges help set expectations:

• Seasonal tune-up: $90–$200
• Capacitor or contactor: $120–$400
• Blower motor: $400–$900
• Defrost board or sensors: $300–$700
• Refrigerant leak find/fix and recharge: $350–$1,200+ depending on leak location
• Reversing valve replacement: $650–$1,500+
• Duct sealing (typical home): $1,000–$3,000

If the system is old and inefficient, a replacement with a high HSPF2/SEER2 variable-speed heat pump may lower bills and runtime, often aided by utility rebates and tax credits.

Preventive Maintenance And Settings That Reduce Runtime

Maintenance Schedule

Smart Thermostat Tips For Heat Pumps

• Enable heat pump mode: Many thermostats have a specific heat pump configuration to manage AUX heat properly.
• Set cycles per hour to 2–3: Avoid overly frequent cycling that reduces efficiency and comfort.
• Use gradual setpoints: Large temperature jumps can trigger AUX heat; use schedules instead of manual swings.
• Adaptive recovery: Let the thermostat start earlier at low stage to reach setpoint on time without AUX.
• Balance humidity: In summer, keep 45–55% RH. Some thermostats allow dehumidification priority that may extend runtimes slightly for comfort.

Home Upgrades That Help

• Air sealing: Caulk and weatherstrip doors and windows; seal attic penetrations and top plates.
• Insulation: Upgrade attic to current recommendations; address knee walls and rim joists.
• Window treatments: Add shades, low-e films, or exterior shading on sun-exposed glass.
• Duct improvements: Seal and insulate ducts outside the conditioned space to cut losses.
• Zoning or balancing: If some rooms lag, a zoning retrofit or duct balancing can reduce overall runtime.

Energy Use, Efficiency, And What’s “Normal” Runtime

Heat pumps are most efficient when allowed to run steadily at lower compressor speeds. A variable-speed unit that operates most of the day at low stage can be more efficient than a single-stage unit cycling on and off. The key is whether it maintains comfort without excessive AUX heat.

Watch energy bills and temperature stability. Sudden increases in kWh, persistent AUX operation above freezing, or longer-than-usual defrosts suggest a problem worth investigating.

Cold-Climate And Regional Considerations In The U.S.

In the Southeast and Mid-Atlantic, humid winters cause frequent frost and defrost. Expect more visible steam and slightly longer runtimes near freezing. In the Northeast and Upper Midwest, cold-climate heat pumps with variable-speed compressors can maintain capacity well below 0°F, but older units may need frequent AUX heat.

In the Southwest and West Coast, cooling loads dominate. Long summer runtimes often indicate solar gain, attic heat, or duct losses rather than equipment failure. Local climate shapes what “normal” looks like for runtime.

Safety And Best Practices

• Power off before cleaning: Turn off breakers or the disconnect before touching the outdoor unit.
• Do not chip ice: Use warm water gently if needed; never pry with tools that can damage coils or fans.
• Keep clearance: Maintain vegetation and fencing 2–3 feet from the unit for proper airflow.
• Use correct filters: High-MERV filters can restrict airflow if the system is not designed for them.
• Avoid repeated breaker resets: If a breaker trips twice, stop and call a professional.

Frequently Asked Questions

Is it bad if my heat pump runs constantly? Not necessarily. Variable-speed systems often run most of the day efficiently. Concern arises if comfort is poor, AUX is on frequently above freezing, or energy use spikes.

How long should a heat pump run per cycle? In mild weather, cycles might be 10–20 minutes. In extreme weather, cycles can be very long or nearly continuous. Continuous low-stage operation can be normal for variable-speed units.

Why does my heat pump blow cool air in winter? Supply air from heat pumps feels cooler than furnace air, often 85–100°F. That’s normal. If air is room temperature or colder for extended periods, check AUX heat, filter, and call a pro if needed.

What is Emergency Heat? A manual setting that forces electric heat strips or backup heat only. Use it if the outdoor unit fails or ices over and call for service. Do not use it for routine heating; it’s expensive to run.

How often should defrost occur? In humid, freezing weather, every 30–90 minutes is common. Short, infrequent defrosts in dry, cold air are also normal. Excessive or ineffective defrosts suggest sensor or control issues.

Will a smart thermostat fix constant running? It can optimize cycles and AUX heat usage, but it won’t compensate for low refrigerant, duct leaks, or undersizing. Pair smart controls with maintenance and home improvements.

Glossary Of Heat Pump Terms

• HSPF2: Heating Seasonal Performance Factor (updated test). Higher is more efficient in heating.
• SEER2: Seasonal Energy Efficiency Ratio (updated test) for cooling efficiency.
• Balance Point: Outdoor temperature where heat pump output equals home heat loss.
• AUX Heat: Automatic backup heat, often electric, used when the heat pump can’t keep up.
• Defrost Cycle: Temporary reverse operation to melt frost on the outdoor coil.
• Reversing Valve: Component that switches between heating and cooling modes.
• Subcooling/Superheat: Measurements used to verify correct refrigerant charge.

Key Takeaways To Reduce Constant Runtime

• Confirm what’s normal: Long, low-stage operation can be efficient and expected.
• Optimize the thermostat: Use heat pump mode, 2–3 cycles per hour, and moderate setpoints.
• Restore airflow: Replace filters, open vents, and clean coils and the outdoor area.
• Address the envelope: Air seal and insulate to reduce heating and cooling load.
• Fix mechanical issues: Low refrigerant, defrost problems, or electrical faults require a pro.
• Schedule maintenance: Annual tune-ups prevent many causes of excessive runtime.