Air-to-water heat pumps are engineered to operate efficiently even in cold weather. However, during frigid temperatures, it’s not uncommon for the outdoor unit to freeze over. While some ice buildup is normal, excessive or persistent freezing can signal a problem that reduces heating efficiency or leads to system damage.

In this guide, we explain why heat pumps freeze, what to do if yours does, and how to prevent freezing in the future.

❄️ Why Do Heat Pumps Freeze in Winter?

Heat pumps extract heat from outside air—even in freezing temperatures. During this process, moisture in the air can condense and freeze on the outdoor coil. Normally, the system enters defrost mode periodically to melt this ice. However, several factors can interfere with this cycle, including:

• Inadequate defrost settings

• Faulty sensors or controls

• Poor airflow or blocked coils

• Low refrigerant levels

• Extreme cold combined with high humidity

️ What to Do If Your Heat Pump Is Frozen

✅ Step 1: Don’t Force It Into Cooling Mode

Some homeowners mistakenly try to melt ice by switching the system to cooling mode. This can cause further damage. Instead, follow these safe steps:

✅ Step 2: Turn Off the Unit Temporarily

Switch off the heat pump at the thermostat and breaker. Allow the ice to thaw naturally, or use warm—not hot—water to gently melt surface frost. Never use a hammer or sharp object.

✅ Step 3: Check for Blocked Airflow

Inspect the outdoor unit for obstructions, such as:

• Snow accumulation

• Ice blocking intake vents

• Leaves, debris, or clogged filters

Clear the surrounding area (at least 2 feet of clearance) for proper airflow.

✅ Step 4: Inspect the Fan and Coils

If safe to do so, check that:

• The fan spins freely

• The coils are not caked in frost or debris

If coils are heavily iced or fan blades are stuck, contact a technician.

✅ Step 5: Verify the Defrost Cycle

Modern heat pumps use sensors and control boards to detect frost and automatically enter defrost mode. If defrost doesn’t activate:

• The sensor may be faulty or dirty

• The control board may need resetting

• The reversing valve or timer could be malfunctioning

These issues require professional inspection.

✅ Step 6: Schedule Professional Maintenance

If freezing is a recurring issue, have a certified HVAC technician:

• Check refrigerant levels

• Test defrost components

• Inspect the reversing valve

• Confirm proper system sizing and airflow

How to Prevent Heat Pump Freezing in the Future

✅ Conclusion

A heat pump freezing in winter is often a sign of maintenance or airflow issues. While some frost is normal, thick ice that doesn’t melt during defrost mode requires action. Follow the steps above to safely resolve minor icing, and contact a technician if freezing persists.

Proactive maintenance and proper installation are the best ways to keep your air-to-water heat pump running efficiently all winter long.