Heat Pump Not Heating in Sunnyvale, CA

Heat Pump Not Heating in Sunnyvale

Most of the heat pump trouble we see in Sunnyvale is heating, not cooling, and it tends to show up the first genuinely cool week of the year. The unit runs, the fan moves air, but what comes out of the registers is lukewarm. People assume the system is dead. In a town where the heating design temperature is around 36 degrees, it almost never is. A heat pump that cannot heat at 40 degrees outside has a specific failed component, not a capacity problem. Sunnyvale winters sit comfortably inside the range these units are rated for.

Two patterns trace back to Sunnyvale's older housing. Plenty of the heat pump conversions in the 1950s and 60s ranches reused the original furnace's air handler and bolted on electric backup heat strips. When the strips fail or never engage, the homeowner feels a heat pump that seems weak on the coolest mornings even though the compressor side is fine. The other pattern is a reversing valve that sticks, leaving the system stuck in cooling mode while the thermostat calls for heat. That one feels dramatic. The house gets colder while the unit runs. But it is usually a stuck valve or a failed solenoid, not a dead system.

On the newer inverter equipment going into Sunnyvale homes, heating faults lean more toward controls: a defrost board reading the outdoor coil wrong, or a low refrigerant charge that throttles capacity. Either way, we treat a heat pump that quit heating as a diagnosis. We measure before we quote, and the fix is usually one part on the written estimate.

Common causes

Reversing valve stuck in cooling. The reversing valve is what flips a heat pump between heating and cooling. When it sticks or its solenoid coil fails, the thermostat calls for heat but the system keeps running in cooling, so the house gets colder while the unit runs. We confirm it by reading line temperatures on both sides of the valve and checking the solenoid for voltage and resistance. The fix is usually the solenoid coil or freeing a stuck valve, occasionally the valve body itself.

Backup heat strips not engaging. Many Sunnyvale furnace-to-heat-pump conversions kept electric resistance strips for the coldest mornings and for defrost. When a strip element, its sequencer, or the limit switch fails, you get a heat pump that feels underpowered on the one cold week of the year. We meter each element and the sequencer, and replace the failed component. The compressor side is often perfectly healthy.

Low refrigerant charge. A heat pump moves less heat into the house when it is low on refrigerant, and low charge almost always means a leak, not normal consumption. We measure superheat and subcooling, find the leak with electronic detection or dye, repair it, then weigh in a correct charge. We put the leak location and the charge numbers on the written estimate so you are not paying to refill a system that will leak out again.

Defrost control fault. In heating mode the outdoor coil collects frost and the unit periodically reverses briefly to clear it. A failed defrost board or coil sensor either skips defrost, so the coil ices and heat output drops, or runs defrost constantly and never settles into heating. We verify the sensor reading against actual coil temperature and check the board's cycle logic before replacing either part.

Failed capacitor or contactor. If the outdoor unit is silent on a heat call, the run capacitor or the contactor is a common culprit. A weak capacitor leaves the compressor or fan straining or not starting; a pitted contactor will not close the circuit. Both are quick to test with a meter and inexpensive to replace, and they are the first things we rule out when the outdoor fan is not turning.

Oversized conversion on an expanded house. Sunnyvale's classic trap is a 1960s ranch with an addition or second-story pop-up still served by undersized original equipment. A heat pump put on that system can short-cycle and never satisfy the upstairs on a cool morning. This is a sizing and zoning problem, not a broken part. We run a Manual J on the real conditioned square footage and tell you honestly whether it is a repair or a sizing fix.

How we diagnose it

Confirm the actual symptom: is the compressor running, is the outdoor fan turning, and what is the supply air temperature versus the thermostat setpoint.
Read line temperatures across the reversing valve to confirm the system is actually switching into heating.
Meter the run capacitor, contactor, and any backup heat strips and sequencers for the outdoor unit and air handler.
Check superheat and subcooling to judge refrigerant charge, and look for ice on the outdoor coil pointing to a defrost fault.
Verify the defrost board logic and outdoor coil sensor reading before condemning any control component.

$75 diagnostic, credited toward any repair over $200. You get a written quote before any work begins.

Heat Pump Not Heating in Sunnyvale: common questions

Do you cover Sunnyvale, and how fast can you get out?

Yes. We work the South Bay including Sunnyvale, and out toward Mountain View and Santa Clara, from our San Ramon base. Same-day is best effort, not a guarantee, and a no-heat call gets priority. Call (925) 999-4095 and we will give you an honest window rather than a vague promise.

Sunnyvale winters are mild. Is a heat pump even the right system here?

It is well matched. Sunnyvale's heating design temperature is around 36 degrees, far inside the range a standard high-efficiency heat pump handles at full rated capacity. You do not need cold-climate equipment here. If your heat pump cannot heat on a 40-degree morning, that is a failed part to repair, not a sign the system is wrong for the climate.

The air coming out feels cool even though the system is running. What does that mean?

Heat pump supply air is normally cooler than a gas furnace, around 90 to 105 degrees, so cool-feeling air is not always a fault. Cold air with the system running usually points to a stuck reversing valve, a low charge, or backup heat strips that failed to engage. We measure supply temperature against the setpoint to tell whether it is normal operation or a real failure.

Nearby and related

Heat Pump Not Heating near Sunnyvale: Mountain View · Santa Clara · Cupertino .

This is usually a heat pump installation & service in Sunnyvale job. See our heat pump installation & service overview or the Sunnyvale service area.