What should I do if my heat pump is not defrosting?

What this symptom usually means

A heat pump is supposed to frost lightly in cold, damp weather, then clear itself during automatic defrost. This page is about the system failing at that second step: the frost does not melt off on its own, ice keeps coming back after you thaw it, or the outdoor unit becomes heavily iced over and heating performance drops. That points specifically to a defrost-cycle problem, not just a general heating complaint.

What you can tell from what you see outside

A thin, even coating of white frost on the outdoor coil in heating mode can be normal for a while. Heavy ice on the grille, fan opening, copper lines, or the entire cabinet is not normal, especially if airflow indoors feels weak or the home temperature slips. If you hear the unit run for long stretches in cold weather without any period where steam rises and the ice clears, the defrost controls are a likely suspect.

If the ice disappears after warm weather or after being thawed, then returns within a day or two of heating use, that pattern often fits a failed defrost board, a bad coil sensor, or a reversing valve that is not shifting. If the outdoor fan is not spinning normally, starts and stops, or the coil is packed with leaves, lint, or cottonwood, airflow issues move higher on the list. If the unit has been heating poorly for a while before the icing started, low refrigerant or another sealed-system fault becomes more likely.

What a technician usually checks on a defrost complaint

On a service visit, the contractor will usually inspect how much of the outdoor unit is iced, check whether the outdoor fan is operating correctly, and test whether the system can enter and complete a defrost cycle. They may measure the defrost sensor or thermostat, verify the control board output, confirm whether the reversing valve energizes, and check refrigerant pressures and temperatures. If the unit is badly encased in ice, some visit time is spent safely thawing it before accurate testing can begin.

What affects repair cost

Cost depends heavily on which part of the defrost system failed and whether the ice is a symptom of a larger heat-pump problem. Defrost sensors, thermostats, and some control boards are often less expensive repairs than a reversing valve or a refrigerant leak, which can involve sealed-system diagnosis, refrigerant recovery, and more labor. Typical 2025-2026 U.S. repair estimates are roughly $150-$450 for some sensors or simple electrical fixes, $300-$900 for many control board or fan-related repairs, and $1,000-$2,500+ for reversing valve or refrigerant-leak repairs depending on access, refrigerant type, and parts availability.

Until it is repaired, many homeowners use emergency or auxiliary heat so the heat pump does not keep trying to run with ice buildup. That can keep the home warm, but it usually costs more to operate than normal heat-pump heating. HVAC Rescue can help arrange an appointment with an independent local contractor, but pricing, timing, and repair approach depend on that contractor and your equipment.