Heat Pump Not Heating in Foster City

Heat Pump Not Heating in Foster City

A heat pump that will not heat often comes down to the same reversing valve, only stuck in the other direction, or a defrost cycle that never completes and leaves the outdoor coil iced over. Low refrigerant, a failing outdoor fan motor, or a corroded contactor and capacitor can all shut heating down the same way they would shut down cooling. We check mode, defrost, and charge in that order before opening anything mechanical. The detail that matters in Foster City is the fill soil settling under the ductwork and the damp lagoon-front air.

Local climate and housing age both matter for a heat pump heating call. Foster City is built almost entirely on filled marshland reclaimed from the bay starting in the 1960s, laced with the lagoons the city is known for, and the lagoon-adjacent air runs damp even on a mild day. The housing is unusually uniform for the Peninsula: 1960s and 70s tract construction on engineered fill, much of it lagoon-front or a short walk from the water. Sixty years of settling in that fill soil has shifted more than a few slabs, which shows up as duct runs that no longer sit level and condensate lines that no longer drain the way they were installed.

In Foster City, we check mode, defrost, and refrigerant charge in that order, because a heat pump that won't heat is rarely one single obvious thing. Whatever the sequence turns up goes on a written estimate, and the $99 diagnostic fee is credited toward the repair.

Common causes

Corroded contactor or capacitor on the outdoor unit. The same electrical parts that fail on an AC condenser fail on a heat pump's outdoor unit. The damp, bay-adjacent air here is harder on exposed electrical connections than a drier inland spot would be. A failed capacitor or a pitted contactor keeps the outdoor unit from running at all.

Stuck reversing valve. A reversing valve stuck in cooling mode leaves the system unable to produce heat no matter what the thermostat calls for. It is one of the first things we rule in or out.

Low refrigerant from a corroded coil or fitting. A leak drops the charge low enough that the system cannot pull adequate heat from the outdoor air, and a corroded fitting is a common leak point. The damp, bay-adjacent air here is harder on exposed electrical connections than a drier inland spot would be.

Failed defrost control. In cold, damp conditions the outdoor coil ices over and the system has to periodically defrost it. A failed defrost board or sensor leaves the coil frozen solid, which blocks heat transfer entirely.

Seized or failing outdoor fan motor. Without the outdoor fan moving air across the coil, the system cannot pull heat from the outside air efficiently, and a seized motor is a common, testable failure.

How we diagnose it

• Confirm the thermostat is actually calling for heat and the system is in heat-pump mode, not stuck on emergency or off.
• Read line temperatures at the indoor and outdoor coils to tell whether the reversing valve has actually shifted into heating.
• Meter the capacitor and inspect the contactor for wear. The damp, bay-adjacent air here is harder on exposed electrical connections than a drier inland spot would be.
• Read refrigerant pressures against the outdoor temperature to spot a low charge before chasing the leak.
• Confirm the defrost board initiates a cycle and the outdoor coil is clear of ice.

$99 diagnostic, credited toward the repair. You get a written quote before any work begins.

Heat Pump Not Heating in Foster City: common questions

Nearby and related

Heat Pump Not Heating near Foster City: San Mateo · Belmont · Redwood City .

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