A heat pump in San Leandro works all year: it cools in summer and runs in reverse to heat in winter. That makes it easier to diagnose than it first appears. If it cools but will not heat, the fault is almost always in the parts that switch modes or handle defrost. If it fails in both modes, the cause is usually shared: airflow, electrical parts, the compressor circuit or refrigerant. We start by working out which group the fault belongs to, then test the parts in it.
Normal or a problem?
Heat pumps do a few things that worry owners the first winter. This table separates the normal from the faults.
| What you see | Normal? | What it means |
|---|---|---|
| Steam rising from the outdoor unit | Normal | Defrost is melting frost off the coil |
| A whoosh, then the outdoor fan stops for a few minutes | Normal | The unit is switching into or out of defrost |
| Light frost on the outdoor coil on a cold, damp morning | Normal | It should clear on the next defrost |
| Thick ice that covers the coil and stays | Not normal | Defrost control, sensor, fan or refrigerant fault |
| Air from the vents feels lukewarm | Usually normal | Heat pump air is warm but cooler than furnace air |
| Thermostat shows aux or backup heat for long periods | Not normal | The heat pump is not keeping up or not running |
| Outdoor unit runs in heat mode but blows cool air inside | Not normal | Often a reversing valve or thermostat setup issue |
Common faults and what they usually take
- Not heating. A stuck reversing valve, a failed valve solenoid, a defrost board fault or a thermostat configured for the wrong type of heat pump. A new thermostat that was wired or set up incorrectly is a surprisingly common cause.
- Not cooling. The same electrical parts as an air conditioner: capacitor, contactor and fan motor, plus a dirty outdoor coil or low refrigerant from a leak.
- Frozen coils. Outdoors in heat mode, usually defrost control or a sensor. Indoors in cool mode, usually low airflow from a dirty filter or blower, or a low refrigerant charge.
- Short cycling. Clogged filters, a thermostat in the wrong spot or with the wrong settings, an oversized system or an electrical fault.
- Strange noises. Rattles from loose panels or debris in the fan, grinding from failing motor bearings, buzzing from a failing contactor or capacitor.
- Defrost problems. A unit that never defrosts ices up; one stuck in defrost blows cool air and leans on backup heat.
Backup heat and the thermostat
Most ducted heat pumps have backup heat: electric heat strips in the indoor unit, or a gas furnace in a dual-fuel system. It is meant to help briefly, during defrost or when you raise the setting by several degrees. The Emergency heat setting turns the heat pump off and runs only the backup, which is useful if the outdoor unit has failed but expensive to leave on. If your thermostat shows aux heat most of the time, have the system checked; your bill will rise long before the house feels cold. If the thermostat itself is the problem, see thermostat installation.
Before you call: safe checks
- The thermostat is in Heat or Cool mode as needed, not Emergency heat by accident.
- The filter is clean, and supply and return grilles are open.
- The breakers for the indoor and outdoor units are on, and the outdoor disconnect is in place.
- Nothing is blocking the outdoor unit, and the space under it is clear so melted frost can drain.
Do not chip or pour hot water on ice on the outdoor coil; the fins and tubing are easy to damage. Switch the system to Emergency heat and call.
What affects the price
Most heat pump repairs fall between $99 and $550, with the diagnostic included. Capacitors, contactors, sensors and thermostat setup problems sit at the lower end. Defrost control boards, reversing valve solenoids and fan motors cost more. Reversing valve and refrigerant leak repairs are the largest jobs, and on an older system we will tell you plainly whether they are worth doing. You see the price before any work starts, and repairs carry a 90-day warranty.
Repair or replace?
One failed electrical or control part on a heat pump that otherwise runs well is worth repairing. A failed compressor, a leaking coil or repeated refrigerant repairs on an older system are when it makes sense to price a new heat pump alongside the repair.
Local notes
Winters in San Leandro, San Lorenzo and Castro Valley are mild, so a working heat pump rarely needs much backup heat. Cool, damp mornings near the bay do frost outdoor coils, though, so defrost faults show up here even without hard freezes. If your home also has ductless heads in an addition or an upstairs room, see mini-split repair.