Why is My Heat Pump Not Working? Troubleshooting Cold Weather Issues

Heat pumps are efficient, versatile systems that handle both heating and cooling from a single unit. But Bucks County winters put them to the test in ways that warmer climates never do. When temperatures drop into the low 20s or single digits, heat pumps behave differently than they do during mild weather, and that behavior is frequently mistaken for a malfunction.

This guide covers why your heat pump may not be working correctly in cold weather, which issues you can address yourself, and which ones need a licensed technician.

Understand How Heat Pumps Work in Cold Weather

Before troubleshooting, it helps to understand what a heat pump actually does and why cold weather complicates it.

A heat pump doesn’t generate heat the way a furnace does. Instead, it extracts heat energy from outdoor air and transfers it inside. Even air at 20 degrees Fahrenheit contains usable heat energy. A heat pump finds it, concentrates it, and moves it indoors.

The challenge is that as outdoor temperatures drop, the available heat energy in the air decreases. The heat pump works harder to extract less. Below a certain temperature threshold, typically around 25 to 35 degrees Fahrenheit for standard heat pumps, the system can’t keep up with heating demand on its own. Most systems paired with a furnace or electric resistance backup switch to that backup automatically when temperatures drop that low.

Knowing this helps you distinguish between a heat pump that’s behaving normally under difficult conditions and one that’s actually malfunctioning.

Your Heat Pump Is Running but Not Heating Adequately

If your heat pump runs continuously but your home stays cold, the first question to ask is what the outdoor temperature is. If it’s below 30 degrees Fahrenheit and your backup heat isn’t engaging, that’s likely your primary problem.

Check the emergency heat setting. Most heat pump thermostats have an emergency heat mode that bypasses the heat pump entirely and runs backup heat directly. This setting exists for exactly the situation where temperatures drop below what the heat pump can handle efficiently. Switching to emergency heat during an extreme cold snap gets your home warm while you diagnose whether the heat pump itself has a problem.

Check the backup heat source. If your system uses a gas furnace as backup, verify the furnace is operational. If it uses electric resistance strips as backup, confirm the breaker for those strips hasn’t tripped. Backup heat failure during extreme cold often gets attributed to the heat pump when the pump itself is actually working correctly.

The Outdoor Unit Is Covered in Ice

Some ice on a heat pump’s outdoor unit during winter is completely normal. Heat pumps run a defrost cycle every 30 to 90 minutes to melt frost that builds up on the coils during heating operation. During a defrost cycle, the system temporarily reverses and blows warm air across the outdoor coil. You may notice steam rising from the outdoor unit and feel cool air from your vents for a few minutes. This is normal.

What’s not normal is a unit that’s completely encased in ice, particularly when ice builds up on the sides and top of the unit rather than just the coil surface. Heavy ice accumulation points to one of several problems.

A failed defrost board or defrost sensor prevents the system from running its defrost cycle correctly. Ice builds progressively with each heating cycle until the coil is completely blocked. When the coil is fully iced, airflow stops and the system can no longer transfer heat effectively.

Low refrigerant also causes excessive icing. When refrigerant levels drop, the coil runs at a lower temperature than designed, causing more frost to accumulate faster than the defrost cycle can handle.

Never attempt to remove ice from a heat pump unit with a sharp tool. You’ll damage the coil fins, which are thin aluminum strips that are easy to bend or puncture. Pouring warm water over a moderately iced coil is safe. For heavy ice accumulation, call a technician.

The Heat Pump Is Short Cycling

Short cycling means the system turns on, runs briefly, and shuts off before completing a full heating cycle. Then it restarts a few minutes later and repeats the pattern. This wastes energy, puts excessive wear on the compressor, and fails to adequately heat the home.

Common causes of short cycling in a heat pump include a refrigerant leak that causes pressure to drop below normal operating levels, a dirty air filter that restricts airflow and triggers a safety shutoff, an oversized system that heats the space too quickly and cycles off before proper air distribution occurs, and a failing compressor that can’t maintain the pressure differential needed to complete a full cycle.

Replace the air filter first. A clogged filter is the simplest fix and one that you can handle immediately without a service call. If short cycling continues after a fresh filter, schedule a diagnostic visit.

The Outdoor Unit Isn’t Running at All

If the indoor air handler runs but the outdoor unit doesn’t, the problem is either electrical or mechanical.

Check the breaker for the outdoor unit. Heat pump outdoor units typically have a dedicated double-pole breaker in the main panel. A tripped breaker cuts power to the outdoor unit while leaving the air handler running on its own circuit.

Also check the disconnect box near the outdoor unit. Most installations include a weatherproof disconnect box mounted on the exterior wall near the unit. If the disconnect has been pulled or a fuse inside has blown, the outdoor unit won’t receive power.

If the breaker and disconnect are both intact, the problem is likely a failed contactor, capacitor, or compressor. The contactor is a relay switch that engages the compressor when the thermostat calls for heat. Contactors wear out over time and sometimes fail without warning. Capacitors store and release electrical energy to start the compressor and fan motors. A failed capacitor is one of the most common heat pump repairs and a relatively inexpensive fix at $150 to $350.

The System Is Blowing Cool Air Indoors

A heat pump that blows slightly cool or room-temperature air during a defrost cycle is normal, as explained earlier. But a system that consistently blows cool air during heating mode has a problem.

Refrigerant loss is the most common cause. When refrigerant leaks from the system, the heat pump loses its ability to transfer heat effectively. The system runs, but it can’t extract and deliver heat the way a properly charged system does. A refrigerant leak requires a licensed technician to locate the leak, repair it, and recharge the system to the correct specification.

A reversing valve failure can also cause this symptom. The reversing valve switches the direction of refrigerant flow to change the system between heating and cooling modes. When the reversing valve sticks in cooling mode, the heat pump blows cool air during heating calls. This repair requires a technician and typically runs $300 to $700 for parts and labor.

When to Call a Technician

Handle these yourself: thermostat checks, filter replacement, breaker resets, and switching to emergency heat mode during extreme cold.

Call a technician for: heavy ice accumulation that won’t resolve, persistent short cycling after a filter change, outdoor unit not running after breaker check, refrigerant-related symptoms, error codes on the thermostat or air handler, and any unusual sounds including grinding, screeching, or loud banging from the outdoor unit.

Home Starr Services provides heat pump repair and diagnostic service throughout Bucks County, Philadelphia, Montgomery County, and surrounding areas. The team handles all major heat pump brands and offers same-day and emergency appointments for heating failures during cold weather. Call 215-510-9017 or check HVAC pricing for current service rates.