A heat pump moves heat instead of making it: in winter it pulls heat from the outdoor air into the house, and in summer it runs the other way. In Tiburon, Belvedere and Mill Valley it may spend most of the year heating, and that is when most problems surface, on cool, damp mornings when the outdoor coil frosts over and the defrost cycle has to do its job. Because one set of parts handles both modes, a fault can show up in heating, in cooling, or in both.
What we check
- Reversing valve and its solenoid. This valve switches the direction of refrigerant flow. If it sticks, the system heats when it should cool or cools when it should heat. The solenoid coil is tested electrically before the valve itself is blamed.
- Defrost controls. A defrost board and sensors decide when to melt frost off the outdoor coil. A failed sensor or board leaves the coil frozen and the house cold.
- Refrigerant charge and leaks. Low charge cuts capacity in both modes and can leave the outdoor coil icing in heating. A low charge means a leak, and we look for it rather than topping up. Refrigerant work is done by EPA-certified technicians.
- Electrical parts. Capacitors, contactors and the outdoor fan motor fail on heat pumps much as they do on air conditioners, but they work all year, so they wear sooner.
- Backup (auxiliary) heat. Electric heat strips in the air handler help in cold weather and during defrost. If they fail, the house cools off during every defrost; if they run too often, the electric bill shows it.
- Thermostat setup. Heat pump thermostats must be configured for the reversing valve and the backup heat. A wrong setting can look exactly like a failed part.
Every repair ends with the system run in both heating and cooling.
Normal or not?
| What you notice | Normal? | What it usually means |
|---|---|---|
| Steam and a whoosh from the outdoor unit for a few minutes | Normal | Defrost cycle |
| Supply air feels warm but not hot | Normal | Heat pumps deliver lower air temperatures than furnaces |
| Outdoor coil stays covered in ice | Not normal | Defrost fault, low charge or outdoor fan problem |
| Heats fine but won’t cool, or the reverse | Not normal | Reversing valve, solenoid or thermostat setup |
| “Aux” or “Emergency heat” on most of the time | Not normal | Lost capacity, refrigerant leak or a setting error |
| Breaker trips when the compressor starts | Not normal | Capacitor, contactor, motor or compressor fault |
Ducted and ductless
Ducted heat pumps use an air handler and your ducts, much like a furnace. Ductless systems use wall, floor or ceiling units in each room. The approach to the repair is the same; the parts and error codes differ. For wall-mounted systems, see mini-split repair.
Repair or replace?
Many people who search for a heat pump replacement actually need one part. A capacitor, a sensor, a defrost board or a reversing valve solenoid is a repair. Replacement makes more sense when the compressor fails on an older unit, when the outdoor coil has corroded through and leaks, when the system still uses R-22, or when the same problem keeps returning. If it is time, heat pump installation covers both ducted and ductless options, and we can give you the repair price and the replacement price side by side.
Local notes
On the Tiburon peninsula and in Belvedere, salt air corrodes outdoor coils, fan motors and electrical terminals faster than inland, and a corroded coil is a frequent source of slow leaks. In Mill Valley, shaded lots under the redwoods keep the outdoor unit damp and in heating mode for long stretches. The local pages cover heat pump repair in Mill Valley, Tiburon and Belvedere. For other heating systems see heating repair, and for cooling-only systems AC repair.