Your heat pump ran perfectly all summer. Now it is January and the indoor unit is blowing air that feels lukewarm at best. Or the display shows a code. Or the outdoor unit is covered in ice and the system stopped running entirely.

Heat pump heating problems in winter are different from summer cooling problems, and when you are searching for heat pump not heating Quincy MA solutions, the refrigerant circuit runs in reverse, different components are under stress, and one of the most common “failures” is actually normal operation that just looks like a problem. This guide covers every scenario, starting with the one you should check before calling anyone.

Check This First | It Is Probably Defrost Mode

Before assuming your heat pump is broken, confirm whether it is in defrost mode.

During winter heating operation, outdoor coil temperatures drop below freezing during normal operation. Ice builds on the outdoor coil. The heat pump periodically reverses the refrigerant cycle to melt this frost, this is called the defrost cycle, and it is completely normal.

During defrost, several things happen that look like a malfunction:

The outdoor fan stops running. The outdoor unit may steam or produce vapor as frost melts. The indoor unit temporarily pushes slightly cool or room temperature air instead of warm air. Some units activate auxiliary heat (if installed) during defrost to maintain indoor temperature.

A defrost cycle lasts 5 to 15 minutes. After it completes, the system returns to normal heating operation. If what you are experiencing resolves within 15 minutes and the system returns to producing warm air, it was a defrost cycle, not a failure.

If the system never returns to producing warm air after 15 minutes, proceed through the checks below.

Step by Step Troubleshooting | Heat Pump Not Heating in Quincy

Step 1 | Check the Thermostat or Remote Mode

Confirm the system is in Heat mode. Mini split remotes are easy to switch modes accidentally, confirm you see a sun or the word “Heat” on the display, not a snowflake or “Cool.” For central heat pump systems, confirm the thermostat is set to Heat and the temperature setpoint is above the current room temperature by at least 4 degrees.

Step 2 | Check the Outdoor Unit

Inspect the outdoor unit. A light frost coating on the coil during cold weather is normal. A solid block of ice encasing the entire unit is not, it indicates the defrost system is not functioning correctly.

If the unit is heavily iced: turn the system off. Do not attempt to remove ice with a sharp object or pour hot water on the unit. Leave the system off for several hours in temperatures above freezing or switch to emergency heat if your system has it. Call a technician, a non functioning defrost system needs diagnosis.

Clear any snow that has built up around or on top of the outdoor unit. Heat pumps need unrestricted airflow on all sides. A unit buried in snow cannot pull adequate air across the coil.

Step 3 | Check the Air Filter

A clogged air filter reduces airflow enough to cause the indoor coil to behave abnormally in heating mode, producing reduced output and, in some cases, triggering protection faults that stop heating operation. Replace or rinse the filter before proceeding to more complex checks.

Step 4 | Check for Error Codes

Mitsubishi, Daikin, and Fujitsu mini splits display fault codes when they detect a heating mode problem. Note the exact code and call a technician with that code, it allows us to arrive with the correct diagnostic approach and likely parts. Common heating mode codes include pressure faults, reversing valve faults, defrost sensor errors, and communication errors.

Step 5 | Assess the Output Temperature

If the system appears to be running in heating mode but the air feels only slightly warm, this is the symptom pattern for low refrigerant in heating mode or a partially stuck reversing valve.

Hold your hand near a supply vent or mini split indoor unit during operation. The air should feel noticeably warm, supply air temperature in heating mode should be 90 to 110 degrees F from a properly functioning system at outdoor temperatures above 20 degrees F. Air that feels barely warmer than room temperature despite the system running indicates a refrigerant or reversing valve issue. Call for a service visit.

The Most Common Causes of Heat Pump Heating Failure in Quincy

Refrigerant Leak | Low Charge in Heating Mode

This is the most common cause of reduced heating performance we see in Quincy heat pump systems. A slow refrigerant leak develops over one or two seasons, often starting as a small leak at a flare fitting that gets worse with thermal cycling.

The critical pattern: the system often cools adequately in summer when refrigerant demand is lower, but struggles to heat in winter when the refrigerant circuit operates at higher pressures. A homeowner calls in January saying “the heat pump stopped working”, but in retrospect, the efficiency had been declining since the previous winter.

Refrigerant leak repair and recharge for heat pump systems in Quincy runs $250 to $600 depending on leak location and quantity of refrigerant needed.

Reversing Valve Fault

The reversing valve is the component that switches the refrigerant circuit direction between cooling and heating mode. A stuck or failing reversing valve leaves the system locked in one mode regardless of the thermostat setting, or partially positioned between modes, which produces neither effective heating nor cooling.

Symptoms: system blows cool air when set to heat (valve stuck in cooling position), or system blows warm air when set to cool (valve stuck in heating position). Reversing valve solenoid coil replacement, often the actual failure point rather than the valve itself, costs $200 to $350. Full reversing valve replacement runs $450 to $700.

Defrost System Fault

If your heat pump runs for a few minutes in heating mode, the outdoor coil ices over completely, and then the system shuts down on a fault, the defrost control board or outdoor temperature sensor has likely failed. The defrost cycle that should prevent coil icing is not initiating.

Defrost board replacement: $250 to $550. Outdoor temperature sensor: $85 to $175.

Outdoor Unit Completely Iced Over

If the outdoor unit has become a solid block of ice, the defrost system has been non functioning long enough for ice to accumulate to the point of blocking all airflow. The system shuts down. This is not a standalone failure, it is the result of an underlying defrost fault that was not caught earlier.

Resolution: let the ice melt naturally or with gentle warm water (never hot water, never sharp objects). Identify and repair the underlying defrost fault before running the system again.

Standard Heat Pump Running Out of Capacity in Cold Weather

This is not a failure, it is a specification issue. Standard (non cold climate) heat pumps lose significant heating capacity below 30 degrees F. On a 15 degree night in Quincy, a standard heat pump may produce only 60 to 70 percent of its rated heating output.

Cold climate heat pump models, Mitsubishi Hyper Heat, Daikin Aurora, Fujitsu XLTH, maintain full rated output to 5 degrees F. If you have an older or lower efficiency heat pump that struggles on cold Quincy nights, this is a specification limitation, not a repair issue. The solution is eventual system replacement with a cold climate model. See heat pump installation details →

Quincy Specific Heating Factors

Coastal salt air on outdoor units. In Wollaston, Marina Bay, Squantum, Adams Shore, and Houghs Neck, outdoor heat pump units accumulate salt deposits on condenser fins year round. A fouled coil in heating mode reduces heat transfer efficiency and can cause the system to struggle at the outdoor temperatures where a clean unit would perform well. Annual coil cleaning before the heating season (September or October) prevents this.

Power outages from winter storms. Quincy’s coastal exposure makes it susceptible to power outages during winter nor’easters. When power returns after an outage, apply the 3 minute rule, wait three minutes before restarting the heat pump. Power restoration without the delay can cause hard start conditions that stress the compressor.

Pre war homes and heat pump sizing. Older Quincy homes with poor insulation and original single pane windows require more heating capacity than their square footage suggests. A heat pump that is correctly sized for a well insulated home of the same size may be undersized for a 1920s colonial in Wollaston without weatherization improvements. A Manual J load calculation before installation prevents this mismatch.

Heat Pump Heating Repair Cost in Quincy MA

Frequently Asked Questions