A heat pump moves heat instead of making it. In summer it pumps heat out of the house; in winter it pulls heat from the outdoor air and brings it inside. The same compressor, outdoor coil, refrigerant charge and reversing valve do both jobs, so a fault often shows up as “heats but won’t cool” or the other way round. Most problems we find in Fremont, Newark and Milpitas homes come down to the reversing valve, the defrost system, a refrigerant leak, an electrical part or a thermostat that was never set up for a heat pump. Our EPA-certified technicians handle the refrigerant side, and same-day service is usually possible.
Common symptoms and what they usually mean
| What you notice | Likely cause | What it usually takes |
|---|---|---|
| Cool air in heat mode, or warm air in cool mode | Reversing valve stuck or its coil failed; thermostat set for the wrong O/B terminal | Thermostat check, valve coil test, valve replacement in worse cases |
| Outdoor coil iced solid | Defrost board or sensor fault, low airflow, low refrigerant | Defrost test, sensor replacement, leak search |
| Outdoor unit hums but the fan does not turn | Failed capacitor or fan motor | Capacitor or motor replacement |
| Backup (“aux”) heat runs constantly, high electric bill | Thermostat settings, low charge, or the outdoor unit not running | Control setup, refrigerant and compressor checks |
| Weak heating and weak cooling | Refrigerant leak, dirty coils or a clogged filter | Leak repair, coil cleaning, airflow check |
| Error code on the wall control or outdoor board | Sensor, communication or inverter board fault | Reading the code and testing the part it points to |
| Water around the indoor unit in summer | Clogged condensate drain | Drain clearing and float switch check |
When refrigerant is low, there is a leak. We find it and fix it rather than topping the system off and leaving it to leak again.
Defrost: normal or a problem?
On cold, damp winter mornings, frost forms on the outdoor coil while the heat pump is heating. Every so often the system switches into defrost: it briefly runs in cooling mode, the outdoor fan stops, and the coil warms up enough to shed the frost, sometimes with a cloud of steam and a whoosh when it switches back. Backup heat may come on for those few minutes so the house does not get a blast of cool air. That is all normal.
Not normal: a coil that stays white or encased in ice, ice building up on top of the unit, or a heat pump that never goes into defrost at all. Do not chip the ice off, because the fins and tubes are easy to damage. Switch the system to Off, or to Emergency heat if it has backup heat and the house is getting cold, and call us.
Heat pump service and maintenance
Because a heat pump runs through both seasons, it builds up more running hours each year than an air conditioner that only cools. A service visit covers:
- Cleaning and inspecting the outdoor coil, and checking the indoor coil, blower and filter
- Testing the reversing valve in both heating and cooling
- Running a defrost test and checking the defrost sensor
- Testing capacitors, the contactor and the electrical connections
- Checking refrigerant performance from temperatures and pressures
- Clearing the condensate drain
- Checking the backup heat strips, if you have them
- Reviewing the thermostat’s heat pump settings
Spring and fall are the right times. Our HVAC maintenance page lists what each visit includes for every type of system.
Smart thermostats and inverter heat pumps
Many of the “broken heat pump” calls we see start at the wall. A smart thermostat on a heat pump has to be set up as a heat pump, with the right reversing-valve setting (O or B) and a sensible limit on when backup heat may run. Get these wrong and the system heats when it should cool, or runs expensive electric strips on mild nights. Inverter (variable-speed) heat pumps and ductless systems often report a fault code on their own control or app. Write it down or take a photo before resetting anything, because a reset can clear it. For ductless systems, see mini-split repair; for setting up controls, our smart home guides.
Before you call: safe things to check
- The thermostat is on Heat or Cool, not on Emergency heat unless you chose it on purpose.
- The filter is clean and the return grilles are not blocked by furniture.
- The breakers for the indoor and outdoor units are on, and the outdoor disconnect is in place.
- The outdoor unit has clear space around it and no leaves packed against the coil.
When repair stops making sense
A failed capacitor, sensor, defrost board or drain is a normal repair on any age of heat pump. A failed compressor, a leaking coil on an older system, or repeated refrigerant leaks is when we price a replacement next to the repair. See heat pump installation.
Local notes
Heat pumps here heat from November to March and cool through the hot afternoons from June to September, so they rarely get a real off-season. Milpitas townhomes often have rooftop or side-yard condensers; let us know about roof access or a gate code when you book. City pages: Fremont, Newark, Milpitas.