No air from the vents or indoor head
The thermostat is calling for heat, but the indoor unit does not seem to blow air at all.
Start here: Start with thermostat mode and setpoint, then check breakers and whether the indoor air handler has power.
HVAC Troubleshooting
Heat Pump Not Heating
Direct answer: If a heat pump is not heating, the most common homeowner-level causes are thermostat settings, a dirty heat pump air filter, restricted airflow, a tripped breaker, or an outdoor unit that is not running or is stuck in heavy ice.
Most likely: Start by confirming the thermostat is in heat mode with the set temperature above room temperature, then check the heat pump air filter, supply airflow, and whether both the indoor and outdoor sections are operating.
Heat pumps can fail to heat in a few lookalike ways: no airflow at all, airflow that feels cool or only mildly warm, heat that works briefly then stops, or an outdoor unit covered in ice. Separating those patterns first helps you avoid guessing and buying the wrong part.
Don’t start with: Do not start by replacing electrical parts, adding refrigerant, or opening access panels around live components.
No airflow from vents?Check thermostat calls, breaker status, and whether the indoor air handler is running before focusing on the outdoor unit.
Airflow is present but house stays cold?Check filter condition, return and supply blockage, outdoor unit operation, and heavy frost or ice on the outdoor coil.
Last reviewed: 2026-03-17
What kind of no-heat problem do you have?
Air is moving, but it feels cool or barely warm
The system runs, but the air does not feel hot like a furnace and the room temperature does not rise.
Start here: Check the heat pump air filter, open vents, return airflow, and whether the outdoor unit is running normally.
Outdoor unit is iced up
You see frost or thick ice on the outdoor coil or cabinet while the system is trying to heat.
Start here: A light frost can be normal, but heavy ice that does not clear points to a defrost, airflow, or service issue. Stop at basic checks and escalate early.
Heat works briefly, then stops or struggles in cold weather
The system starts heating, then seems to lose output, short cycle, or cannot keep up.
Start here: Check for a dirty filter, blocked airflow, thermostat scheduling issues, and signs the outdoor unit is shutting down or not defrosting properly.
Most likely causes
1. Thermostat settings or scheduling issue
A thermostat in cool, auto-changeover confusion, emergency heat misunderstanding, low batteries, or a schedule setback can make the system appear to have failed.
Quick check: Set the thermostat to heat, raise the setpoint at least 3 to 5 degrees above room temperature, and wait several minutes for the system to respond.
2. Dirty heat pump air filter or blocked airflow
Restricted airflow can reduce heat output, cause coil temperature problems, and make the system run without warming the house well.
Quick check: Inspect the heat pump air filter and make sure return grilles and supply registers are open and not blocked by furniture or rugs.
3. Power loss to the indoor or outdoor section
A heat pump needs both indoor and outdoor components working together. If one side loses power, you may get no airflow, weak heat, or room-temperature air.
Quick check: Check the main electrical panel for tripped breakers and look for a nearby outdoor disconnect that appears off or partially pulled out.
4. Outdoor unit defrost or refrigeration problem
If the outdoor coil is heavily iced, the outdoor fan is not operating correctly, or the system has a refrigerant or control issue, heating performance drops sharply.
Quick check: From a safe distance, see whether the outdoor unit is running, whether there is only light frost or heavy ice buildup, and whether the unit makes unusual noises or repeatedly stops.
Step-by-step fix
Step 1: Confirm the thermostat is actually calling for heat
Thermostat mode, setpoint, and scheduling errors are common and safe to rule out first.
- Set the thermostat to heat mode, not cool or fan-only.
- Raise the target temperature at least 3 to 5 degrees above the current room temperature.
- If the thermostat has batteries and the screen is dim, replace the batteries.
- If there is a programmed schedule, temporarily override it so the system should run now.
- Wait several minutes to allow any built-in delay to finish.
Next move: If the system starts and warm-up begins, the problem was likely a setting, schedule, or weak thermostat battery issue. If nothing changes, move to airflow and power checks before assuming a failed component.
What to conclude: This separates a simple control issue from a true heating or equipment problem.
Stop if:
- The thermostat display is blank and does not recover after basic battery replacement.
- You smell burning, see sparking, or hear buzzing from the thermostat or equipment.
- The system trips a breaker as soon as heat is called for.
Step 2: Check the heat pump air filter and basic airflow
Poor airflow is one of the most common reasons a heat pump runs but does not heat well.
- Turn the system off at the thermostat before removing the filter.
- Inspect the heat pump air filter for heavy dust, pet hair, or collapse.
- Replace a dirty disposable filter or clean a washable filter only if the manufacturer allows it and it is fully dry before reinstalling.
- Make sure return grilles are not blocked and supply registers are open.
- Check that the indoor coil area and vents are not being choked by obvious dust buildup or stored items around the unit.
Repair guide: How to Replace a Heat Pump Air Filter
What to conclude: A clogged filter can reduce heating output on its own and can also contribute to icing and poor defrost performance.
Stop if:
- You find water around the indoor unit, signs of ice inside the cabinet, or damaged wiring.
- The filter is wet, moldy, or the blower area is inaccessible behind service panels.
- The indoor unit makes grinding, screeching, or strong burning smells.
Step 3: Make sure both the indoor and outdoor sections have power
A heat pump cannot heat normally if the indoor air handler or the outdoor unit has lost power.
- Check the home's electrical panel for any tripped HVAC-related breakers.
- If a breaker is tripped, reset it once only by switching it fully off and then back on.
- Look at the outdoor disconnect only from the outside to see whether it appears off, missing, or partially pulled out.
- After restoring power, call for heat again and listen for the indoor blower and outdoor unit to start.
- If the breaker trips again, stop troubleshooting and arrange service.
Repair guide: How to Reset An HVAC Breaker Safely
Stop if:
- A breaker trips more than once.
- You see scorched insulation, melted wire covering, or smell electrical burning.
- You would need to remove electrical covers or test live voltage to continue.
Step 4: Check the outdoor unit for normal operation versus heavy icing
This separates normal cold-weather behavior from a defrost or service problem.
- With the thermostat still calling for heat, observe the outdoor unit from a safe distance.
- A light, even frost can be normal for a while; thick ice coating the coil, fan guard, or base is not.
- Listen for whether the outdoor fan runs smoothly or whether the unit hums, clicks, or starts and stops repeatedly.
- If the unit is buried in leaves, snow drift, or debris, gently clear space around it without prying on fins or using sharp tools.
- Do not chip ice, pour hot water on the unit, or force a defrost cycle from internal controls.
Repair guide: How to Clean a Heat Pump Outdoor Unit Exterior
Stop if:
- The outdoor unit is heavily iced over and the system keeps trying to run.
- You hear loud buzzing, hard starting, metal scraping, or repeated clicking.
- You suspect refrigerant loss or see oily residue around refrigerant lines or the outdoor coil area.
Step 5: Decide whether this is a simple maintenance fix or a service call
By this point you should know whether the problem was settings, airflow, or a higher-risk equipment fault.
- If the thermostat correction or heat pump air filter replacement solved the issue, keep monitoring system performance over the next day.
- If the system runs but still cannot maintain temperature, note whether the outdoor unit runs, whether ice forms, and whether airflow is weak or normal.
- If your system has an emergency heat setting, use it only as a temporary comfort measure if the manufacturer and thermostat support it, understanding it may cost more to operate.
- Arrange service if the breaker trips again, the outdoor unit ices heavily, one section will not run, or heating remains poor after the basic checks.
- When you call, describe the exact pattern: no airflow, cool airflow, heavy ice, breaker trip, or outdoor unit not running.
A good result: If the home warms normally and the system cycles as expected, no further action may be needed beyond routine maintenance.
If not: If the system still does not heat after these checks, the remaining likely branches are not good guess-and-buy DIY repairs.
What to conclude: This keeps you from replacing the wrong part when the real issue may be defrost controls, a blower problem, refrigerant loss, or another service-level fault.
Stop if:
- You are relying on repeated breaker resets to keep heat on.
- The system is producing burning smells, smoke, or unusual vibration.
- You would need to open sealed refrigerant components or diagnose live electrical parts to continue.
Replacement Parts
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FAQ
Why is my heat pump running but not blowing hot air?
Heat pumps usually deliver air that feels warm but not furnace-hot. If the house is not warming, common causes are a dirty heat pump air filter, blocked airflow, thermostat issues, power loss to one section, or an outdoor unit that is iced up or not operating correctly.
Is some frost on a heat pump normal in winter?
Yes. A light frost on the outdoor coil can be normal in heating mode. Thick ice covering much of the coil, fan area, or cabinet is not normal if it persists, and that points to a defrost, airflow, or service problem.
Should I reset the breaker if my heat pump is not heating?
You can check for a tripped breaker and reset it once. If it trips again, stop there. Repeated breaker trips suggest an electrical or equipment fault that needs professional diagnosis.
Can a dirty filter really make a heat pump stop heating well?
Yes. A clogged heat pump air filter can reduce airflow enough to cut heating performance, contribute to icing, and make the system run longer without raising room temperature effectively.
Should I add refrigerant if my heat pump is not heating?
No. Refrigerant is not a basic DIY fix. Low refrigerant usually means there is a leak or another service issue, and adding refrigerant without diagnosis can hide the real problem and create safety and equipment risks.
When should I call for service instead of troubleshooting more?
Call for service if the breaker trips again, the outdoor unit is heavily iced, one section will not run, you smell burning, or the system still cannot heat after thermostat, filter, airflow, and basic power checks.