Heat pump not blowing warm air? Causes, fixes, and when to call a pro

If your heat pump stops delivering warm air, the house can feel like a fridge overnight. Most homeowners assume it’s a major failure and call a technician immediately, but a lot of the time the issue is something you can diagnose and even fix yourself. Below you’ll find a plain‑English walk‑through of how a heat pump works, the most common culprits behind cold‑air complaints, a step‑by‑step troubleshooting checklist, and clear signs that it’s time to bring in a professional.

How a heat pump actually moves heat

Understanding the system helps you spot where it’s breaking down. A Heat pump is a refrigeration‑based unit that extracts heat from the outdoor air (even when it’s chilly) and delivers it inside via a refrigerant cycle consists of two main sections: the outdoor unit and the indoor air handler. The outdoor unit houses the compressor, condenser coil, and a reversing valve that flips the refrigerant flow depending on heating or cooling mode. Inside, the air handler contains an evaporator coil, a fan motor, and the ductwork that pushes air into your rooms.

Top reasons why warm air isn’t coming out

Below are the most frequent issues you’ll encounter. Each one includes a quick visual cue so you can decide whether to keep going or pick up the phone.

• Thermostat the control panel that tells the heat pump when to heat or cool is set to the wrong mode or temperature.
• Air filter a replaceable screen that traps dust and debris is clogged, restricting airflow.
• Compressor the heart of the outdoor unit that compresses refrigerant, raising its temperature has failed or is overheating.
• Reversing valve a valve that switches the refrigerant flow for heating versus cooling is stuck in the cooling position.
• Outdoor unit the external box containing the compressor, coil, and fan is covered in ice or debris, reducing heat exchange.
• Fan motor drives the indoor blower that pushes air through ducts isn’t spinning or is running at low speed.
• Refrigerant the fluid that circulates through the system to transport heat is low or has leaked.
• Ductwork leaks or blocked vents are preventing warm air from reaching rooms.

Step‑by‑step troubleshooting guide

1. Check the thermostat. Make sure it’s set to “Heat” and the temperature is higher than the current room temperature. Reset the thermostat by turning it off for 30 seconds.
2. Inspect the indoor air filter. If it looks dark or crammed, replace it. A clean filter restores proper airflow and can solve the problem instantly.
3. Listen for the outdoor unit. You should hear a faint hum and the fan running. If the compressor is silent or makes a buzzing sound, turn off power at the breaker, wait five minutes, then restart. Persistent silence indicates a compressor fault.
4. Look at the outdoor coil. If you see frost covering more than half the coil, the defrost cycle may be stuck. Turn the system to “Cool” for a few minutes-this often clears excess ice.
5. Open the front panel of the indoor air handler and locate the fan motor. Verify it spins freely when the system is on. A squealing or stalled motor usually needs lubrication or replacement.
6. Check the reversing valve indicator light (if your model has one). A solid green usually means heating mode; a flashing or red light can indicate a valve problem.
7. If you suspect a refrigerant leak, look for oily spots near the connections. Leaks are a job for a licensed technician because handling refrigerant requires certification.
8. Walk through each vent. Close all but one and feel the airflow. If the open vent is warm but others are cold, you likely have duct leaks that need sealing.
9. After each step, run the heat pump for 10‑15 minutes and note any change in air temperature. Documenting results helps you or a technician pinpoint the exact failure point.

When to call a professional

Even if you enjoy DIY, some problems are best left to experts, especially in a city like Toronto where the climate swings between sub‑zero winters and warm springs. Call a licensed HVAC contractor if you encounter any of the following:

• The outdoor unit won’t start at all after resetting the breaker.
• You smell refrigerant (a sweet, chloroform‑like odor) or see oil on the coil.
• The system cycles on and off rapidly (short‑cycling), which can damage the compressor.
• Electrical components such as capacitors or contactors appear burnt or broken.
• You’re unsure about handling refrigerant or need a pressure test.

Professional service typically includes a full system pressure test, component diagnostics, and warranty‑covered repairs.

Maintenance tips to keep warm air flowing

Regular upkeep prevents most of the cold‑air scenarios listed above. Schedule these tasks at least twice a year-once before the heating season and once after.

• Replace or clean the indoor air filter every 30‑60 days during heavy use.
• Trim shrubs and leaves away from the outdoor unit to maintain clear airflow.
• Check the condensate drain line for clogs; a blocked line can trigger a safety shut‑off.
• Run the system in “Fan‑Only” mode for a few minutes each month to keep the indoor blower lubricated.
• Record the date of any professional service; a service log helps technicians diagnose recurring issues faster.

Quick comparison: Common symptom vs likely cause vs quick fix

Frequently Asked Questions