Heat Pump Not Heating? Start With These Simple Checks
If your heat pump is not heating, first check that the thermostat is set to Heat, the temperature is above the current room temperature, and the fan is set to Auto. Then replace a dirty filter, make sure supply vents are open, and clear leaves, snow, or ice away from the outdoor unit. If the system is still blowing cold air, repeatedly trips a breaker, makes unusual noises, or stays iced over, turn to emergency heat only as a short-term backup and call an HVAC technician.
A brief blast of cool air is not always a failure. Heat pumps normally deliver air around 85 to 95 degrees Fahrenheit, which can feel lukewarm compared with furnace heat. They may also switch into a defrost cycle for about 5 to 15 minutes to melt frost on the outdoor coil.
The usual causes range from a thermostat setting or clogged filter to low refrigerant, a stuck reversing valve, failed auxiliary heat, or an electrical problem. This guide helps you sort out the safe checks you can make yourself and the warning signs that need professional repair.
At All-Temp Heating & Cooling, our team has spent more than 15 years helping homeowners in the Shenandoah Valley solve heat pump heating problems, from simple airflow issues to complex winter system failures.
Why Is Your Heat Pump Not Heating? 8 Common Causes
Unlike a traditional furnace that burns fuel to create heat, a heat pump absorbs heat from outside air and moves it indoors. When one part of that transfer process fails, system capacity can drop quickly.
Identifying the component causing your heating loss helps you determine whether you can make a safe DIY adjustment or need professional tools.
1. Thermostat Settings and O/B Reversing Valve Wiring
The thermostat acts as the brain of your heating system. Many heating service calls trace back to simple control issues or incorrect configuration after a new smart thermostat installation.
- Incorrect mode or fan setting: If the thermostat fan is set to On instead of Auto, the indoor blower runs continuously even when the heat pump is not actively warming the air. This circulates room-temperature air between heating cycles, making vents feel drafty and cold.
- Mismatched O/B terminal logic: Heat pumps use an internal valve to switch between heating and cooling. Most systems energize the reversing valve in cooling mode, often called the “O” setting, while some brands energize it during heating, often called the “B” setting. If configured incorrectly, your heat pump can blast cold air when calling for heat.
- Compressor lockout thresholds: Smart thermostats often have minimum compressor temperature settings. If set improperly, the thermostat may shut off the outdoor compressor too early during mild cold snaps.
2. Clogged Air Filters and Restrictive Airflow
Adequate airflow across both indoor and outdoor coils helps the system move heat into your home. When air cannot move freely, the system cannot absorb or distribute heat throughout your rooms.
A dense layer of dust on an air filter restricts the air passing over the indoor evaporator coil. This restriction raises static pressure, limits warm air delivery, and can trip high-limit safety switches that shut down heating elements.
To avoid common heat pump maintenance mistakes, inspect filters monthly and replace standard 1-inch pleated filters every 30 to 60 days during peak winter heating cycles.
3. Faulty or Stuck Reversing Valve
The reversing valve redirects the flow of refrigerant, allowing the heat pump to switch between cooling mode in the summer and heating mode in the winter.
If the internal sliding mechanism inside the reversing valve binds up, or if the electrical solenoid coil controlling it fails, the heat pump remains locked in cooling mode. You might hear electrical buzzing or repetitive clicking or buzzing noises coming from the outdoor cabinet as the unit attempts to shift. When this occurs, the outdoor unit will run, but the vents will supply room-temperature or chilled air.
4. Low Refrigerant Charge and System Leaks
Heat pumps rely on a sealed charge of chemical refrigerant, such as R-410A, to absorb and carry heat. Because the system is closed, refrigerant is never “used up” or consumed during normal operation.
When a pinhole leak develops in copper lines or aluminum coils:
- The system’s operating pressure drops below factory specifications.
- The outdoor coil cannot absorb enough heat from the outside air.
- Ice begins forming along the refrigerant lines and indoor coil.
- The compressor runs continuously without raising indoor temperatures.
Adding refrigerant without sealing the leak is only a temporary repair. An EPA-certified technician must locate the leak, repair the tubing, pull a deep vacuum, and recharge the system to exact factory weight.
5. Outdoor Unit Icing and Defrost Board Malfunctions
During winter, moisture in the air condenses on the outdoor coil and freezes into frost. Under normal conditions, the heat pump’s control board starts a defrost cycle every 30 to 90 minutes when outdoor temperatures drop below 40 degrees Fahrenheit.
A standard defrost cycle lasts 5 to 15 minutes. During that time, the system temporarily reverses into cooling mode to send warm refrigerant into the outdoor coil and melt frost. If the defrost control board, relay, or temperature sensor fails, the unit cannot melt this frost.
Ice can build up until thick sheets cover the outdoor coil, block air intake, and stop heat production. Our heat pump defrost mode guide explains how these controls protect your system during cold Shenandoah Valley weather.
6. Defective Auxiliary Heat Strips
When outdoor temperatures drop below freezing, standard heat pumps rely on supplemental electric resistance heat strips, also called auxiliary heat, inside the indoor air handler to satisfy the thermostat setpoint.
If these heating elements fail due to broken coils, failed thermal sequencers, or a tripped dedicated air-handler breaker:
- The heat pump will continue running its outdoor compressor.
- Supply air will remain lukewarm, often 85°F to 95°F, instead of reaching the warmer 100°F-plus temperatures provided by auxiliary heat.
- The indoor temperature will slowly decline during overnight cold snaps.
Failed heat strips can make a system seem fine during mild afternoons but weak during cold nights in Staunton, Harrisonburg, Waynesboro, and nearby areas.
7. Electrical Issues and Tripped Breakers
Heat pumps require significant electrical current and use two high-voltage feeds: a dedicated 240V double-pole breaker for the outdoor compressor and fan, and a separate 240V breaker for the indoor air handler and heat strips.
If the outdoor breaker trips due to an electrical surge, weakened run capacitor, or worn motor winding, the indoor blower might continue circulating unheated air through your home. Always check both the main panel breakers and the outdoor disconnect switch near the condensing unit. If a breaker trips again, leave it off and schedule professional heat pump services so our team can test the equipment safely.
8. Extreme Cold Exceeding the Thermal Balance Point
Every heat pump installation has a calculated “thermal balance point.” This is the outdoor temperature where the home’s natural heat loss equals the maximum heating output of the heat pump.
- Heat pump efficiency and heating capacity decrease when outdoor temperatures drop below 35 degrees Fahrenheit.
- Standard air-source heat pumps lose capacity once temperatures fall into the teens.
- If your home has drafty windows or unsealed crawlspaces, heat loss can outpace heat production.
Understanding the balance point helps determine the ideal heating options for Virginia homes, especially in mountain climates where dual-fuel hybrid systems provide supplemental furnace heat on sub-freezing nights.
Fast Troubleshooting Steps for Homeowners
Before scheduling a service diagnostic, follow these straightforward checks to rule out external setup errors.
Safe DIY Checklist for a Heat Pump Not Heating
Follow these actionable troubleshooting steps in order:
- Verify thermostat settings: Ensure the system mode is set to HEAT, not Cool or Off, and the setpoint temperature is at least 3 degrees above the current room temperature. Set the fan switch to AUTO.
- Inspect the air filter: Remove and inspect the central return filter. If it is coated with dust, hair, or debris, install a fresh replacement with the correct airflow direction arrows.
- Check circuit breakers: Locate your main electrical panel. Look for tripped double-pole breakers labeled “Heat Pump,” “AC,” or “Air Handler.” Reset a tripped breaker firmly to OFF, then back to ON once. If it trips again immediately, leave it off and call a technician.
- Examine the outdoor cabinet: Walk outside and inspect the heat pump. Ensure there is at least 2 feet of clear space around the unit. Clear away drifted snow, piled leaves, or encroaching shrubbery.
- Check supply and return registers: Walk through your home and verify that interior supply vents and large return air grilles are unobstructed by furniture, heavy rugs, or drapes.
- Observe for defrost operation: If the outdoor unit is lightly frosted and blowing cool air indoors, wait 15 minutes. If steam rises from the outdoor unit and warmer air returns shortly after, the system was performing a normal defrost cycle.
Auxiliary Heat vs. Emergency Heat: When to Use Backup
Many homeowners confuse auxiliary heat with emergency heat, leading to unexpectedly high power bills.
- Auxiliary heat (AUX): This is an automatic staging function. Your thermostat turns on the electric resistance heat strips alongside the heat pump compressor when the outdoor temperature drops below the balance point, or when you raise the thermostat setpoint by 3 or more degrees.
- Emergency heat (EM HEAT): This is a manual user setting. Switching to Emergency Heat locks out the outdoor heat pump entirely and runs only the electric resistance heat strips inside the air handler.
Because electric resistance heat functions like a large electric toaster, emergency heat can use 2 to 3 times more electricity than normal heat pump heating. Only engage Emergency Heat if the outdoor unit has suffered a total mechanical failure or is locked out due to severe damage.
Professional Repair vs. Replacement Costs
When DIY troubleshooting points toward a failed mechanical or electrical component, professional service is required. Our licensed team can test electrical components, check refrigerant pressures, and perform targeted heat pump repair in Harrisonburg.
Component Repair Considerations
The table below outlines common repairs required when a heat pump stops heating, along with standard repair considerations:
| Failed Component | Function in Heating Mode | Repair / Replacement Considerations |
|---|---|---|
| Thermostat / wiring | Directs system staging and mode switching | Recalibration, wiring corrections, or control board replacement. |
| Defrost control board | Monitors coil frost and manages defrost cycles | Board replacement and defrost temperature sensor calibration. |
| Reversing valve solenoid | Provides electrical charge to shift internal valve | Low-voltage electrical replacement without opening refrigerant lines. |
| Reversing valve body | Channels high-pressure refrigerant flow | Requires refrigerant recovery, brazing in new valve, and system recharge. |
| Refrigerant leak repair | Restores proper system operating pressures | Electronic leak detection, line repair/brazing, and fresh refrigerant. |
| Electric auxiliary heat strip | Supplies supplemental and backup heat | Sequencer replacement, thermal limit reset, or new element restringing. |
| Run capacitor / contactor | Starts and provides stable power to compressor | Electrical testing and replacement of failing high-voltage switches. |
When to Replace an Aging Heat Pump
A heat pump typically lasts 12 to 15 years with proper maintenance. As equipment approaches the end of its design life, major component repairs become less economical.
Consider investing in a new system if:
- The system has exceeded 12 years of age and requires a major component repair, such as a compressor or reversing valve.
- Your winter utility bills have risen steadily despite regular maintenance.
- The system utilizes obsolete R-22 refrigerant rather than modern refrigerants.
- You notice recurring breakdowns, unusual motor groaning, or multiple signs you need a heat pump replacement.
Frequently Asked Questions About Heat Pump Performance
Why is my heat pump not heating and blowing cold air?
A heat pump blowing cool air in heat mode is usually in a normal defrost cycle, running with the thermostat fan set to On instead of Auto, or experiencing a stuck reversing valve. Heat pumps also deliver air between 85°F and 95°F, which feels cooler to the touch than 120°F furnace air.
Is it normal for heat pump supply air to feel lukewarm?
Yes, this is completely normal. Heat pumps supply air at 85 to 95 degrees Fahrenheit. Because your natural body temperature is 98.6 degrees, air blowing across your skin at 90 degrees can feel slightly cool or lukewarm, even though it is actively warming a 68-degree room.
Why does my heat pump run constantly without reaching the set temperature?
During freezing weather, heat pumps run for long cycles because they extract smaller amounts of heat over extended periods. However, if the system runs nonstop without raising room temperature in mild weather, above 40°F, common causes include dirty air filters, low refrigerant charge, leaky ductwork, or failed auxiliary heat strips.
Restoring Your Heat Pump’s Heating Performance
A heat pump that struggles to heat your home during freezing winter weather can stem from simple issues like dirty air filters and incorrect thermostat modes, or complex problems like refrigerant leaks, failed heat strips, and frozen coils. Performing basic checks helps you resolve minor setting issues quickly, while recognizing normal operational quirks, such as mastering heat pump defrost cycles, prevents unnecessary service calls.
If troubleshooting your thermostat, filters, and circuit breakers does not restore steady warmth to your home, contact our professional heat pump repair technicians at All-Temp Heating & Cooling to inspect your system and restore dependable comfort.