Most heat pump repair comes down to a short list of parts: the run capacitor and contactor in the outdoor unit, the defrost control board and its coil sensor, the reversing valve, the outdoor fan motor and the refrigerant charge. Many failures show up first as a coil buried in ice, a system stuck on auxiliary heat, or cold air in heat mode. Some of what looks like a breakdown is normal heat pump behavior, so the first job is telling the two apart.
Normal Heat Pump Behavior That Looks Like a Problem
A heat pump is an air conditioner that can run backward: in winter a reversing valve flips the refrigerant flow so the outdoor coil pulls heat out of cold air (see how a heat pump works for the full mechanics). That design produces a few behaviors that alarm people for no reason.
Defrost mode. Near freezing with damp air, frost forms on the outdoor coil, and the defrost control periodically switches the system into cooling for a few minutes to melt it. The outdoor fan stops, the reversing valve shifts with a loud whoosh, and steam rises off the unit. When defrost ends you hear a second whoosh and the fan restarts. Water and slush on the pad afterward are expected.
Long run times in cold weather. Capacity drops as the outdoor temperature drops, so running nearly nonstop on the coldest days is by design.
Air that feels lukewarm. Heat pump supply air is often in the 90s Fahrenheit, well below furnace air. It feels cool on your hand while still heating the house.
Aux heat in very cold weather. Below a certain outdoor temperature, the balance point, a standard heat pump can no longer keep up alone and the backup strips help. Cold-climate models with variable-speed compressors hold out much longer before that happens.
Heat Pump Symptoms and Likely Causes
| Symptom | Likely causes | Who handles it |
|---|---|---|
| Solid block of ice covering the coil and top of the unit that never clears | Failed defrost board or coil sensor, stuck reversing valve, dead outdoor fan motor, low refrigerant, or water dripping on the unit from a gutter | Homeowner clears the gutter or drainage issue; technician for the rest |
| Cold air from the vents in heat mode | Thermostat setup, reversing valve stuck in cooling, outdoor unit not running, low charge | Homeowner checks settings; technician for the valve or charge |
| Aux or emergency heat running all the time in mild weather | Outdoor unit down (capacitor, contactor, tripped breaker), low refrigerant, thermostat set to Emergency Heat or configured wrong | Homeowner checks the thermostat and breakers; technician for electrical or refrigerant faults |
| Outdoor fan runs but the compressor hums or clicks off | Weak run capacitor, failing contactor, hard-starting compressor | Technician |
| Outdoor unit completely dead | Tripped breaker or disconnect, failed contactor, low-voltage control fault | Homeowner resets breaker once; technician if it trips again |
| Works in cooling but not heating, or the reverse | Reversing valve solenoid coil, valve stuck, wrong O/B thermostat setting | Technician; homeowner can confirm the thermostat setting |
| Hissing, oily spots on copper lines, steadily falling performance | Refrigerant leak | Technician with EPA Section 608 certification |
What You Can Safely Check Before Calling Anyone
- Thermostat mode and setup. Confirm it is on Heat, not Emergency Heat, and that the setpoint is above room temperature. If the thermostat was just replaced, a wrong O/B reversing valve setting will give you cooling when you ask for heat. See heat pump thermostat wiring for how those terminals work.
- Air filter. A clogged filter cuts airflow, which raises head pressure in heating and can trip safeties.
- Breakers and the outdoor disconnect. A heat pump usually has one breaker for the outdoor unit and another for the air handler and heat strips. Reset a tripped breaker once. If it trips again, leave it off.
- Clearance around the outdoor unit. Clear snow, leaves and drifted debris so the coil can breathe, and keep roughly two feet clear on all sides. Make sure the unit sits high enough that defrost water can drain away instead of refreezing around the base.
- Water from above. A leaking gutter or roof edge dripping onto the unit will freeze into a solid cap that no defrost cycle can clear. Fixing the gutter fixes the ice.
- Watch a defrost cycle. If the coil frosts and then clears, the defrost system works.
If the outdoor unit is encased in ice, switch the thermostat to Emergency Heat (see emergency heat vs aux heat for how the two modes differ). That stops the outdoor unit and keeps the house warm on the strips until the ice melts or a technician arrives. Do not chip or pry at the ice: the fins and tubes puncture easily, turning an iced coil into a refrigerant repair.
What not to touch. Do not open the electrical panel on the outdoor unit. Run capacitors store enough charge to injure you even after the power is off. Do not push in the contactor by hand, swap reversing valve wires, or add refrigerant from a store-bought can. Opening or charging the refrigerant circuit requires EPA Section 608 certification, and an incorrect charge damages the compressor.
What Heat Pump Repair Involves
A proper diagnosis covers both halves of the system: thermostat calls and low-voltage wiring, voltage and amperage at the outdoor unit, the capacitor against its rating, and pressures and temperatures in heating, cooling or both.
Capacitor and contactor. The most common failures on any outdoor unit, and a quick swap that leaves the refrigerant circuit closed.
Defrost board and coil sensor. The tech can force a defrost cycle through test pins on the board. If the unit does not enter defrost, the problem is the board, the sensor clipped to the coil, or the reversing valve. A sensor is usually tested and replaced first because it is cheaper.
Reversing valve. If the solenoid coil on the valve has failed, it is an electrical swap. If the valve body itself is stuck or leaking internally, it has to be cut out and a new one brazed in. That means recovering the refrigerant, protecting the new valve from heat, purging with nitrogen, pulling a deep vacuum and recharging by weight.
Refrigerant leaks. A good repair finds the leak with an electronic detector, bubbles or a nitrogen pressure test, repairs it, and then recharges. Topping off without finding the leak only delays the next call.
Compressor. Before condemning a compressor, the technician should rule out the capacitor, contactor and wiring and check the windings. A compressor that will not start is sometimes helped by a hard-start kit, though that is a stopgap on an aging unit. For more detail, see compressor repair and replacement.
What Drives Heat Pump Repair Cost
Prices vary too much by region to quote, but the relative order is consistent:
- Low end of the bill: capacitors, contactors, coil sensors, thermostat and low-voltage wiring fixes.
- Middle: defrost control boards, outdoor fan motors, blower motors in the air handler, reversing valve solenoid coils.
- High end: anything that opens the refrigerant circuit, such as leak repairs and reversing valve replacement, and compressor replacement, which is often the single most expensive repair.
Other factors move the number: after-hours dispatch, the type and amount of refrigerant, access to the unit, whether the manufacturer's parts warranty still applies (labor usually is not), and parts availability. Common parts for brands such as Trane, Rheem, Daikin or Mitsubishi are usually on supplier shelves, while some control boards have to be ordered. Geothermal heat pumps cost more to service because the ground loop needs specialized work.
If a quote is heading toward replacement territory, compare it with our heat pump installation cost guide before you approve the repair.
Repair or Replace Your Heat Pump
Heat pumps typically last roughly 15 to 20 years, less in harsh coastal or very cold climates, and a regular heat pump maintenance checklist is the part of that you control. Rules of thumb:
- Under about 10 years old: repair almost anything, and check the warranty first. Many compressors carry a longer parts warranty than the rest of the unit if the system was registered.
- 10 to 15 years: repair small electrical and control faults without much thought. For a compressor, reversing valve or major leak, apply the 50 percent rule: if the repair would cost more than about half of a replacement, replace.
- Over 15 years, or any R-22 system: put major repair money toward a new system. R-22 production ended in the US on January 1, 2020, so the remaining supply only gets scarcer.
Replacing the outdoor unit alone on an older split system is often a poor deal, because a new outdoor unit needs a matched indoor coil and may use a different refrigerant. Our guide to what a heat pump installation involves covers sizing and matching.
How to Vet a Heat Pump Repair Contractor
Questions to ask before you approve work:
- What exactly failed, and how did you confirm it? Can I see the reading or the old part?
- Is the part still under manufacturer warranty, and will you handle the warranty claim?
- Will the refrigerant circuit be opened? If so, how will you find the leak rather than just adding refrigerant?
- Are your technicians EPA Section 608 certified, and is the company licensed and insured where you live?
- Is the estimate written and itemized, and what labor warranty comes with the repair?
- If the problem is ice, did you test the defrost board, the coil sensor and the reversing valve?
Red flags:
- Adding refrigerant every season without a leak search.
- Condemning the compressor without testing the capacitor, contactor and windings.
- Pressure to replace the whole system on the first visit for a fault that is a common, inexpensive part.
- Refusing to put the diagnosis and price in writing.
Ductless systems have their own failure points; see our guide to ductless mini split repair if your heat pump is a wall-mounted unit.
Frequently Asked Questions
Is it normal for a heat pump to ice up in winter?
A thin layer of frost that clears during periodic defrost cycles is normal, and so are the steam and whoosh that come with defrost. A solid block of ice that covers the coil and survives several defrost cycles is not, and points to a defrost, airflow or refrigerant fault.
Why is my heat pump blowing cold air in heat mode?
Heat pump air often leaves the vents in the 90s Fahrenheit, so it feels cooler than furnace air. Air that is genuinely cold usually means the outdoor unit is not running, the reversing valve is stuck in cooling, the unit is defrosting, or the refrigerant charge is low.
Why is my heat pump running on aux heat all the time?
Aux heat normally runs during defrost, after a big setback and in very cold weather. If it runs constantly in mild weather, the outdoor unit is not doing its share, usually because of a failed capacitor or contactor, low refrigerant, a stuck reversing valve or a misconfigured thermostat.
How much does heat pump repair cost?
It depends mostly on which part failed and whether the refrigerant circuit has to be opened. Capacitors, contactors and sensors sit at the low end, defrost boards and fan motors in the middle, and reversing valves, leak repairs and compressors at the high end.
Is it worth repairing a 15-year-old heat pump?
Usually only for a small repair. Heat pumps typically last roughly 15 to 20 years. Fix a capacitor or sensor, but put compressor, reversing valve or major leak money toward a replacement, especially on an R-22 system.
Can I repair my heat pump myself?
You can check the thermostat, replace the filter, reset breakers and clear snow and debris from the outdoor unit. Leave the rest to a technician: capacitors hold a charge even with power off, and refrigerant work requires EPA Section 608 certification.