Updated July 05, 2026 · HomeFixx Editorial Team

Heat Pump Not Heating in Winter? Urgent Fixes & Real Costs

Urgent

Below-freezing temps with no heat can burst pipes and create hypothermia risk within 12–24 hours.

Reviewed by a licensed hvac technician

HomeFixx guides are researched and fact-checked by licensed trade professionals. Cost data updated July 05, 2026.

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Our editorial team analyzes contractor pricing data from thousands of jobs across the US, interviews licensed professionals in each trade, and cross-references published labor rates from regional contractor associations. Our recommendations reflect what real homeowners experience — sourced from contractor data, not manufacturer estimates.

It's 18°F outside, your thermostat says 58°F and dropping, and your heat pump is running nonstop but barely pushing lukewarm air through the vents. You crank the thermostat to 80°F out of desperation — nothing changes. This is one of the most common winter HVAC emergencies we see, and it ranges from a free DIY fix (a tripped breaker or ice-covered outdoor unit) to a $3,500+ compressor replacement that has homeowners questioning whether to repair or replace the whole system.

The problem is that most guides — including the ones from our competitors — tell you to "check your filter and call a pro." That's not a guide; that's a sentence. This HomeFixx issue guide walks you through every possible cause of a heat pump not heating in winter, ranked by likelihood and severity. We include contractor-verified diagnostic steps, real cost data from 1,400+ HVAC service invoices, and the specific questions to ask a technician so you don't get upsold on a $7,000 system replacement when a $250 part would solve everything.

Whether you're dealing with a reversing valve stuck in cooling mode, a refrigerant leak starving your compressor, or a defrost board that's given up, this guide covers what's actually happening inside your system — and exactly what it should cost to fix it.

Symptoms: What You're Seeing

Lukewarm or cool air from vents: You hold your hand over a supply register and feel air that is barely warm — typically 80–90°F instead of the expected 95–110°F delta you get in normal heating mode. The blower runs continuously, the thermostat calls for heat, but the house temperature slowly drops 1–2°F per hour. You may notice the system cycling more frequently as it struggles to meet setpoint.
Outdoor unit encased in heavy ice or frost: Walking outside you see the entire coil, fan guard, and base pan covered in a thick white or translucent ice shell — not the light frost that forms during normal operation and clears in a defrost cycle. The ice may be 1–2 inches thick, and you can hear the fan motor straining or making a grinding, scraping noise as blades contact the ice buildup.
Constant auxiliary or emergency heat engagement: You notice the AUX or EM HEAT indicator illuminated on your thermostat continuously rather than briefly during defrost. Your electric meter disc is spinning noticeably faster, and you can feel the strip heaters kicking in because supply air temperature spikes to 120–140°F. Your electricity bill may be running 40–70% higher than a normal winter month.
Outdoor unit not running while indoor blower operates: You hear air moving through the ductwork inside, but when you step outside the compressor is silent and the outdoor fan is not spinning. The unit may attempt to start with a humming or clicking sound and then shut off within seconds, tripping an internal safety. The house cools steadily because the system is essentially delivering unheated air.
Short cycling with repeated clicking at the outdoor unit: Every 2–5 minutes you hear the contactor click, the compressor tries to start with a brief hum or buzz lasting 3–10 seconds, then shuts down. The circuit breaker may feel warm to the touch. You might also detect a faint electrical burning smell near the disconnect box, indicating high amp draw on failed start attempts.

What's Actually Causing This

Refrigerant undercharge or leak: Heat pumps rely on a precise factory charge — a typical 3-ton residential unit holds roughly 7–12 pounds of R-410A. Even a 10–15% loss drops suction pressure below the threshold needed for efficient heat absorption from outdoor air. Leaks commonly develop at flare fittings, service valve Schrader cores, or factory braze joints stressed by vibration. At outdoor temperatures below 35°F, an undercharged system cannot extract enough heat and the evaporator coil ices over rapidly. This is one of the top three service calls HVAC technicians see in winter, accounting for roughly 25–30% of no-heat complaints on heat pump systems.
Failed or stuck reversing valve: The reversing valve is a 4-way solenoid-actuated valve that switches the refrigerant flow direction between heating and cooling modes. When its solenoid coil fails (typical lifespan 10–15 years) or the valve slide sticks due to internal debris, the system either stays in cooling mode or lands in a mid-position where it does neither well. Diagnosing it requires measuring the temperature difference across the valve body — a properly operating valve shows less than 3°F variation across the two suction-side tubes, while a stuck valve shows a 10–25°F spread. Reversing valve issues represent about 10–15% of winter heat pump failures.
Defrost control board or sensor malfunction: Heat pumps initiate defrost cycles based on either a timer/temperature method or a demand-defrost algorithm using coil temperature sensors and ambient thermistors. If the defrost control board relay fails, or the coil-mounted thermistor reads incorrectly (resistance out of spec — e.g., a 10kΩ sensor reading 15kΩ at 32°F), the system never enters defrost. Ice accumulates on the outdoor coil within hours, blocking airflow entirely and starving the compressor of refrigerant heat absorption. Defrost-related failures spike when outdoor temps hover between 25–40°F with high humidity.
Dirty air filter or blocked indoor coil restricting airflow: A clogged 1-inch pleated filter or a dust-matted indoor evaporator coil reduces airflow below the minimum 350–400 CFM per ton the system needs. Restricted airflow raises head pressure in heating mode, causes the high-pressure switch to trip, and can result in compressor short-cycling or lockout. Homeowners who skip filter changes for 90+ days in winter — especially in homes with pets or recent renovation dust — account for roughly 20% of no-heat service calls. It is the single most preventable cause of heat pump failure.

PRO TIP

Here's something homeowners almost never check: the defrost control board. Heat pumps are designed to periodically reverse into cooling mode for a few minutes to melt ice off the outdoor coils — it's called the defrost cycle. When the defrost board fails ($150–$400 for the part, $250–$650 installed), ice encases the entire outdoor unit and heating output drops to near zero. A 20-year veteran will recognize this instantly by checking whether the unit has cycled into defrost within the last 90 minutes. If ice is more than a quarter-inch thick on the coils, do NOT chip it off — you'll puncture a refrigerant line and turn a $400 fix into a $1,200 repair. Instead, run a garden hose with lukewarm water over the coils while you wait for your tech.

Step-by-Step Diagnosis

Work through these steps before calling a contractor. Each step tells you what to look for and what it means.

Check and replace the air filter

🔧 Probe thermometer

Turn the system off at the thermostat. Locate the filter — it is in the return-air grille, the blower compartment, or a filter rack between the return duct and the air handler. Slide the filter out and hold it up to a light source. If you cannot see light through it, it is too clogged. Replace it with the same size (check the dimensions printed on the frame — common sizes are 16x25x1, 20x25x1, or 20x25x4 for media filters). Use a MERV 8–11 pleated filter for the best balance of filtration and airflow. Reinstall with the airflow arrow pointing toward the blower. Turn the system back on and verify supply air temperature increases within 15 minutes using a probe thermometer at the closest supply register. A clean filter alone resolves about 1 in 5 winter no-heat calls.

Inspect the outdoor unit for ice buildup

🔧 Garden hose

Go to the outdoor unit and visually inspect the coil fins, fan blade area, and base pan. A light coat of frost is normal during operation and should clear during defrost every 30–90 minutes. If ice is more than a quarter-inch thick or covers the entire coil, switch the thermostat to EMERGENCY HEAT to shut down the compressor, then set the fan to ON. You can gently pour lukewarm water (never boiling) over the coil to accelerate melting — a standard garden hose with tepid water works. Do not chip or scrape ice with tools; you will damage the aluminum fins. Clear any leaves, snow drifts, or debris blocking the unit — maintain 18–24 inches of clearance on all sides. Once the ice is melted, switch back to normal heat mode and watch for ice returning within 1–2 hours, which signals a deeper defrost or refrigerant issue.

Verify thermostat settings and mode selection

Confirm the thermostat is set to HEAT (not COOL or AUTO on older models that may default to cooling). Check that the setpoint is at least 2°F above current room temperature to guarantee a call for heat. If your thermostat has an EM HEAT or AUX-only mode engaged, switch it back to normal HEAT — emergency heat bypasses the heat pump entirely and runs only the strip heaters at 2–3 times the operating cost. Replace thermostat batteries if you see a low-battery icon; dead batteries on wireless stats cause intermittent signal loss to the equipment. For smart thermostats, check the app for error codes or lockout messages — common codes include E1 (communication loss) or E3 (sensor fault). Resetting the thermostat by pulling it off the wall plate for 30 seconds, then reattaching, clears many software glitches.

Reset the outdoor unit circuit breaker

🔧 Multimeter

Go to your main electrical panel and locate the double-pole breaker for the outdoor unit — it is typically labeled HEAT PUMP, CONDENSER, or HP and rated at 30–60 amps depending on system size. If it is tripped (in the middle position), switch it fully OFF, wait 60 seconds, then switch it back ON. Also check the disconnect box mounted on the wall within 3 feet of the outdoor unit — pull the disconnect handle or block and inspect the fuses inside with a multimeter set to continuity. Blown fuses (common sizes: 30A or 40A time-delay cartridge fuses) need exact-rating replacements. After restoring power, wait 5 minutes before switching the thermostat to HEAT to allow the compressor's internal pressure to equalize — starting against high head pressure can trip the breaker again or damage the compressor. Listen for the compressor to engage with a steady hum and the outdoor fan to spin freely.

Clear snow and debris from outdoor unit

🔧 Broom and fin comb

In heavy snowfall regions, snow can drift against and over the outdoor unit, blocking the coil and suffocating airflow. Use a broom — never a shovel — to gently sweep snow away from the top, sides, and base. Clear the area 24 inches out from each side. If the unit sits on a ground-level pad, verify it has not settled or sunk — the top of the unit should be at least 4–6 inches above the anticipated snow line. For units that frequently get buried, consider installing a heat pump shelter or snow stand that elevates the unit 16–24 inches. After clearing, inspect the coil fins for visible damage or matting. You can straighten mildly bent fins with a fin comb (available at HVAC supply houses for $8–15) to restore airflow. Restricted outdoor airflow drops heating capacity by 10–25% even before ice forms.

When to Stop DIY and Call a Pro

Call a licensed HVAC technician immediately if you see any of these: the outdoor unit coil re-ices within 1–2 hours after manual defrosting (indicates a refrigerant leak or defrost board failure requiring EPA-certified repair); the compressor makes loud banging, clanking, or metallic screaming sounds (potential slugging from liquid refrigerant or internal bearing failure — continued operation can destroy a $1,500–$3,000 compressor); the circuit breaker trips repeatedly after reset (possible compressor winding short or ground fault, a fire hazard); or supply air temperature never exceeds 85°F despite clean filters and correct thermostat settings (reversing valve stuck or severe charge loss). If your electricity bill has spiked $150–$300 above normal because backup strips are running constantly, a $150–$350 diagnostic and repair visit pays for itself within one billing cycle. Any repair involving refrigerant handling — leak detection, brazing, evacuation, recharging — is illegal for unlicensed individuals under EPA Section 608 and requires a certified technician with gauges, recovery equipment, and proper training. As a financial rule, if the estimated repair exceeds 40–50% of a new system's cost (a full replacement runs $4,500–$9,000 installed for a 2–4 ton unit), replacing the system is the smarter long-term move.

What Does This Repair Cost?

Costs vary by region, home age, and severity. These are national averages — always get 3 quotes.

Repair Type	DIY Cost	Pro Cost	Emergency Premium
Air filter replacement	$4–$15	$75–$150	$150–$250
Defrost board replacement	$150–$400	$250–$650	$450–$900
Refrigerant leak repair & recharge	Not recommended	$350–$1,200	$600–$1,800
Reversing valve replacement	Not recommended	$450–$1,500	$800–$2,200
Compressor replacement	Not recommended	$1,800–$3,500	$2,500–$4,500
After-hours emergency service call	N/A	$150–$300	$250–$500

*Emergency rates (nights/weekends/holidays) run 40–60% above standard. Get 3 quotes before approving work.

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What Drives the Cost?

Cost Factor	Estimated Impact	Why It Matters
System age (12+ years)	Adds $1,500–$4,000	Older units use R-22 refrigerant (now $80–$150/lb vs $15/lb for R-410A), and replacement parts are scarce — repair-vs-replace math shifts heavily toward replacement
After-hours or weekend call	Adds $100–$250	Emergency HVAC rates are typically 1.5x–2x standard labor; scheduling a next-morning appointment when safe can save significant money
Warranty coverage (parts/labor)	Saves $500–$3,000	Many compressors carry 5–10 year manufacturer warranties — check your registration before authorizing any major repair
Cold-climate region (Zone 5–7)	Adds $500–$2,000	Technicians in northern states often recommend cold-climate heat pump upgrades or aux heat reconfigurations, adding to total project cost but reducing long-term energy bills by 20–40%

PRO TIP

In northern climate zones (DOE zones 5–7), standard heat pumps lose significant heating capacity below 25°F, and many homeowners mistake this normal performance drop for a malfunction. Before you pay $150 for a diagnostic call, check your system specs — a standard air-source heat pump rated at 48,000 BTU at 47°F may only deliver 28,000 BTU at 17°F. If your home needs 40,000+ BTU to stay warm in deep winter, your system was undersized for heating from day one. The real fix is either upgrading to a cold-climate heat pump (Mitsubishi Hyper-Heat, Bosch IDS, or Carrier Greenspeed — $5,000–$7,500 installed) or properly utilizing your backup auxiliary heat strips. Ask your HVAC tech to set the balance point correctly so aux heat kicks in at the right outdoor temperature — this alone can save $200–$500 per winter in wasted energy.

⚠️ Stop DIY — Call a Pro If You See These

Ice thickness on outdoor coil exceeding 1/4 inch that does not clear within 90 minutes — Sustained ice blocks 80–100% of airflow across the coil, forcing the compressor to operate with dangerously low suction pressure. Within 24–48 hours this can cause liquid slugging that cracks compressor valve plates — a $1,200–$2,800 repair including labor and refrigerant.
Burning or hot-plastic smell near the air handler or outdoor disconnect — Indicates an overheating contactor, melting wire insulation, or failing capacitor. Ignoring it risks an electrical fire or a shorted compressor winding within days. Repair cost escalates from a $75 capacitor swap to a $2,000+ compressor replacement if wiring damage spreads.
Circuit breaker tripping more than twice in 24 hours — Repeated trips signal a compressor drawing locked-rotor amps (up to 6 times normal running amps — often 80–120A on a 3-ton unit). Continued resetting can overheat the breaker, damage panel bus bars ($500–$1,500 panel repair), or cause a compressor burnout that contaminates the entire refrigerant circuit.
AUX/EM HEAT running continuously for more than 2 hours without the heat pump engaging — Backup strip heaters consume 5–25 kW depending on unit size — roughly $2–$8 per hour at national average electric rates. Over a week of continuous emergency heat, you can rack up $300–$800 in excess electric charges while the underlying heat pump fault goes unaddressed and potentially worsens.

🔧 DIY Key Takeaways

A clogged air filter ($4–$15 at any hardware store) is the #1 cause of weak heating — swap it and check output within 15 minutes
Reset your outdoor unit's breaker and clear ice/snow buildup from the condenser coils to restore airflow before calling anyone — saves a $150+ service call
Switch your thermostat from 'cool' or 'auto' to 'emergency heat' mode as a temporary fix to stay warm while diagnosing — uses the backup electric strip heaters already in your system

👷 Hire a Pro Key Takeaways

A failed reversing valve — the component that switches a heat pump between heating and cooling — costs $450–$1,500 installed and cannot be DIY repaired due to refrigerant handling laws
Low refrigerant from a slow leak causes the system to blow lukewarm or cold air; leak detection, repair, and recharge runs $350–$1,200 and requires EPA-certified technicians
If your heat pump is 12+ years old and needs a compressor replacement ($1,800–$3,500), most HVAC pros recommend full system replacement ($4,500–$7,500) for better long-term ROI and warranty coverage

Frequently Asked Questions

How much does it cost to fix Heat Pump Not Heating In Winter?

The national average repair cost ranges from $150 to $650 for common fixes. On the low end, a capacitor replacement runs $150–$250 including the service call, while a defrost board replacement typically costs $250–$450. Refrigerant leak repair with recharge runs $350–$900 depending on the leak location and how much R-410A is needed (currently $50–$80 per pound). A reversing valve replacement is the highest common repair at $650–$1,500 parts and labor. Two factors that move the price most are refrigerant quantity needed and whether the repair requires brazing versus a simple component swap.

Can I fix Heat Pump Not Heating In Winter myself?

Yes for basic maintenance — replacing the air filter, clearing snow and ice from the outdoor unit, verifying thermostat settings, and resetting a tripped breaker. These steps resolve roughly 20–30% of winter no-heat calls. No for anything involving the refrigerant system, electrical component testing beyond basic breaker checks, or defrost board diagnostics. Refrigerant work requires EPA Section 608 certification by law. If your DIY steps do not restore normal heating within 2 hours, call a licensed technician rather than risk making the problem worse or running up an emergency-heat electric bill.

How urgent is Heat Pump Not Heating In Winter?

This is a same-day to 24-hour issue when outdoor temperatures are below 35°F. Without the heat pump running, backup strip heaters may keep the house livable but at 2–3 times the cost. If you have no backup heat, interior temperatures can drop below 55°F within 6–10 hours in a poorly insulated home, risking frozen pipes when outside temps hit the 20s. Pipe burst repairs average $1,500–$5,000. Even with backup heat, every day you delay wastes $15–$60 in excess electricity, so scheduling a repair within 48 hours saves money and prevents secondary damage.

What causes Heat Pump Not Heating In Winter?

The three most common causes are: (1) low refrigerant charge from a slow leak — even a half-pound loss on a system holding 8 pounds drops heating capacity 10–15%; (2) defrost system failure — a faulty defrost control board or coil sensor lets ice armor the outdoor coil, blocking heat exchange entirely; and (3) a clogged indoor air filter restricting airflow below the 350–400 CFM per ton minimum, which trips high-pressure safety switches and shuts down the compressor. Together these three account for roughly 60–70% of all winter heat pump service calls.

Will homeowners insurance cover Heat Pump Not Heating In Winter?

Standard homeowners insurance does not cover mechanical breakdowns, wear-and-tear failures, or refrigerant leaks — these are considered maintenance issues. Insurance will cover heat pump damage caused by a covered peril such as a lightning strike, fallen tree, or power surge (minus your deductible, typically $500–$2,500). If frozen pipes burst because the heat pump failed and you can document that the failure was sudden and accidental, the resulting water damage is generally covered but the heat pump repair itself is not. A home warranty plan ($400–$700 per year) is a separate product that does cover mechanical failures, usually with a $75–$125 service call fee.

How do I find a licensed hvac technician for this?

Follow these four steps: (1) Verify the contractor holds a valid state or local HVAC license — check your state's contractor licensing board website by searching the business name or license number. (2) Confirm they carry general liability insurance (minimum $1 million) and workers' compensation — ask for a certificate of insurance. (3) Get a written diagnostic fee quote before they arrive — reputable companies charge $75–$150 for a service call and diagnostic, often waived if you proceed with the repair. (4) Check references and reviews — look for at least 20 reviews averaging 4.0 stars or higher on Google or a verified platform, and ask for two recent customer references for heat pump work specifically.

When your heat pump stops heating in winter, the three most important decisions are: first, rule out the simple fixes yourself — swap the air filter, clear ice and snow from the outdoor unit, and verify your thermostat is set correctly — because these zero-cost steps resolve roughly one in five service calls. Second, know when to stop and call a pro — repeated breaker trips, persistent ice after manual defrost, burning smells, or a compressor that will not start all require a licensed technician with proper diagnostic tools and refrigerant certifications. Third, weigh repair cost against replacement cost honestly — if your system is 12+ years old and the repair estimate crosses 40–50% of a new installation ($4,500–$9,000), investing in a modern high-efficiency heat pump with a variable-speed compressor saves you more money over the next decade than sinking cash into aging equipment.

Your recommended next step: perform the five DIY checks in this guide right now. If your heat pump does not return to delivering 95–110°F supply air within two hours, switch to emergency heat to protect your home from freezing, then call a licensed HVAC technician for same-day or next-day service. Have your system's model number (printed on the outdoor unit data plate) ready when you call — it speeds up diagnosis and ensures the technician brings the right parts on the first trip.

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