Is Your Heat Pump Freezing Up in the Winter? Common Causes and Fixes

Did your heat pump turn into a snowman overnight? One common issue homeowners face during winter is a frozen heat pump. While this can be extremely frustrating and lead to temporary comfort issues, the problem is usually fixable in a few hours. However, you may need to hire a professional to repair the root cause of the issue.

HVAC.com explains the causes of a heat pump freezing up in the winter, tips to thaw a frozen heat pump, and preventive measures to keep your system from turning into an ice box again this season.

How Does a Heat Pump Work?

In the summer, a heat pump operates similarly to a central air conditioning system. Cold refrigerant passes through the indoor evaporator coil and extracts warm air from inside your home and turns it into a low-pressure gas that is released into the outdoor air through the condenser coil.

In heating mode, the heat pump operates in reverse – absorbing heat from the outside air through the condenser coil and releasing it indoors through the evaporator coil to provide efficient heating. Even when it’s cold outside, there’s enough heat in the outside air to keep a home warm, although some heat pumps become less efficient when temperatures drop below freezing.

To prevent ice buildup on the outdoor coil during the winter, heat pumps have a defrost cycle. This cycle works by briefly reversing the flow of refrigerant, turning the outdoor coil into an evaporator, which melts any ice accumulation. During the defrost cycle, the system may rely on auxiliary heating to maintain the indoor temperature. The defrost cycle typically runs every 30-90 minutes and lasts about 5 to 15 minutes, depending on the conditions.

What Causes a Heat Pump to Freeze Up in Winter?

Although it’s not unusual for a heat pump to accumulate some ice – especially when there’s snow or freezing rain and the outside temperature drops below 40°F – a heat pump completely encased in ice for several hours is a big problem. It can cause the system to malfunction or fail to start at all.

Here are some of the most common causes of a heat pump freezing up in the winter:

1. Dirty Air Filter

A dirty or clogged air filter is one of the most common causes of a frozen heat pump. A dirty air filter restricts airflow into the system, which can cause the heat pump to work improperly and lead to ice buildup on the outdoor condenser coil. Air filters should be replaced or cleaned every couple of months to ensure proper airflow and prevent freezing.

2. Low Refrigerant Levels

Low refrigerant levels can prevent a heat pump from transferring heat properly. With insufficient refrigerant, the condenser coil’s temperature drops, causing moisture in the air to freeze on the coil, resulting in a frozen heat pump.

3. Malfunctioning Defrost Cycle

The defrost cycle is designed to prevent ice from accumulating on the condenser coil. However, various issues can cause the defrost cycle to fail, including problems with sensors, the control board, or other components. When the defrost cycle doesn’t function properly, the heat pump can freeze up.

4. Outdoor Temperature Extremes

Extremely cold temperatures, particularly below 30°F, can overwhelm a heat pump that isn’t designed to operate efficiently in such conditions. In these situations, the system may struggle to extract heat from the outside air, causing ice to form on the outdoor coil. Rain, snow, or sleet combined with low temperatures can exacerbate the freezing problem.

5. Blocked or Dirty Condenser Coil

If the condenser coil is obstructed by dirt, debris, or snow, the heat pump can’t absorb heat from the outside air as effectively. This lack of heat absorption can also cause the coil to freeze, disrupting the heating process and potentially damaging the system.

6. Faulty Reversing Valve

The reversing valve allows a heat pump to switch seamlessly between heating and cooling modes. If the reversing valve malfunctions, the defrost cycle may fail to engage properly, causing ice to accumulate on the coil and tubing.

7. Damaged Fan Motor

A damaged or malfunctioning fan motor can prevent the outdoor fan from properly circulating air over the condenser coil. Without sufficient airflow, the condenser coil’s temperature drops too low, leading to ice buildup. This lack of airflow may significantly reduce the heat pump’s heating capacity.

8. Excess Moisture

Excess moisture can also contribute to a frozen heat pump. For example, water from a leaking gutter or pooling around the outdoor unit can introduce moisture into the system, causing the heat pump to freeze. When the unit is submerged in or surrounded by standing water, ice forms more quickly, obstructing airflow and further impairing the heat pump’s performance.

How to Unfreeze a Heat Pump

If your heat pump is completely frozen, the first step is to turn the system off to avoid further damage. Next, check for obvious issues, such as a clogged air filter or debris around the unit. Replace the air filter if necessary and clear away any debris to improve airflow and prevent additional freezing.

To thaw the ice, you can gently hose the outdoor unit with water, but avoid using high heat, such as a hairdryer or heat gun, as these can damage the system. Then, turn the heat pump to “fan” mode until all of the ice melts which may take a few hours. If the ice persists or keeps returning, contact a professional HVAC technician. They can inspect the system for issues like a malfunctioning defrost cycle, low refrigerant, or a faulty fan motor.

How to Prevent a Frozen Heat Pump

Preventing a frozen heat pump starts with regular maintenance – both DIY and professional – to address common issues like refrigerant leaks and dirty coils before they become serious problems.

A heat pump tune-up, performed by an HVAC technician, involves cleaning and inspecting all components, ensuring that everything is functioning properly for winter. During the tune-up, the technician will also check the defrost cycle and recommend any needed repairs to prevent future freezing.

In between professional tune-ups, regular DIY maintenance is key to keeping your heat pump in good shape. Here are a few tips for preventing a frozen heat pump:

1. Replace Air Filters Regularly: Change or clean the air filters every 2-3 months to maintain proper airflow. Restricted airflow can lead to ice buildup and other issues, which can be costly to fix.
2. Remove Debris Around the Outdoor Unit: Keep the area around the outdoor condenser free of debris like leaves, snow, or twigs. This ensures proper airflow and allows the system to absorb heat efficiently.
3. Check for Leaks or Standing Water: Ensure that water from damaged gutters is not dripping onto the heat pump and that there is no standing water near the unit. Excess moisture can freeze on the coils and contribute to the problem.

By following these preventive measures and scheduling regular maintenance, you can keep your heat pump running efficiently throughout the winter months.