Heat Pump Not Heating in Mountain View, CA

Heat Pump Not Heating in Mountain View

A lot of Mountain View heat is newer than people think. Old Mountain View ranches that started life with a gas furnace and no AC got converted to heat pumps over the last decade, and the ADU and garage conversions all over town run on ductless mini-splits. Both can stop heating in winter, and the cause is rarely the whole unit. It is one component in a system that is otherwise fine.

The most common version we see: the outdoor unit runs, air moves, but it blows cool or lukewarm. That points at the refrigerant circuit or the reversing valve, the part that flips a heat pump between heating and cooling. On a ductless mini-split feeding an ADU, a stuck reversing valve or a low charge from a slow line-set leak shows up as a room that won't hold its setpoint, no matter how long it runs.

Mountain View winters are mild, with marine-layer mornings and lows that sit comfortably above where a standard heat pump still puts out its rated capacity. So when one stops heating it is a fault, not the climate outrunning the equipment. We find the failed part and put the fix and the price on the written estimate before we touch it.

Common causes

Reversing valve stuck in cooling mode. The reversing valve switches the refrigerant flow direction between heating and cooling. When its solenoid sticks or the valve body hangs partway, the unit keeps running in cooling while the thermostat calls for heat, so you get cool air on a cold morning. We confirm it by reading line temperatures and the solenoid coil. Sometimes the coil is the failure and is a straightforward swap. A seized valve body is a bigger job, and we tell you the cost difference before we start.

Low refrigerant from a line-set leak. ADU and garage-conversion mini-splits often have line sets routed through framing during the build. A slow leak at a flare fitting drops the charge, and heating capacity falls off before cooling does. We pressure-test, find the leak with electronic detection or nitrogen, repair the joint, then weigh in a correct charge rather than just topping it off.

Defrost control not cycling. On our foggy, damp mornings the outdoor coil picks up frost. The defrost board is supposed to reverse briefly and melt it. When that board or its sensor fails, frost builds into ice and heating output collapses. We watch a defrost cycle, check the sensor resistance, and replace the control or sensor that is out of spec.

Failed run capacitor or contactor. If the outdoor unit is silent or hums and won't start, the run capacitor or the contactor is the usual culprit. A weak capacitor reads low on a meter; a pitted contactor won't pull in cleanly. Both are common wear parts we carry on the truck and replace the same visit.

Aux heat not engaging on a ducted conversion. Ducted heat-pump conversions usually have electric backup strips for the coldest mornings. If the heat-pump stage is down and the strips aren't picking up, you get cold air. We verify thermostat staging, the strip relays, and the sequencer so the backup actually carries the load while we sort the primary fault.

How we diagnose it

Confirm the call for heat at the thermostat and watch what each stage actually does, heat-pump stage then any backup.
Read suction and liquid line temperatures and pressures to separate a charge problem from a reversing-valve problem.
Energize and observe the reversing-valve solenoid and run a defrost cycle to see the outdoor coil clear.
Meter the run capacitor and contactor on the outdoor unit for a no-start or short-cycle complaint.
On mini-split ADU installs, inspect the flare joints and line-set routing for the slow leaks those builds are prone to.

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

Heat Pump Not Heating in Mountain View: common questions

Do you cover Mountain View, or only the Tri-Valley?

We are based in San Ramon and cover Mountain View and the rest of the Peninsula and South Bay daily. A no-heat heat-pump call gets prioritized for same-day when we can, though same-day is best effort, not a guarantee. Call (925) 999-4095 and we'll tell you a real window.

Mountain View winters are mild. Could the cold itself be why it stopped heating?

No. Our winters are mild, and a standard heat pump puts out full rated capacity well below the lows we actually see here. If yours stopped heating, a part failed. The mild climate is one reason a single component fix usually restores full performance.

My ADU mini-split blows but the air isn't warm. What is that?

Air moving but not warming almost always means the refrigerant side: a low charge from a line-set leak or a reversing valve stuck in cooling. We measure line temperatures to tell which, then repair the leak and recharge, or address the valve. We don't just add refrigerant and leave.

Nearby and related

Heat Pump Not Heating near Mountain View: Palo Alto · Los Altos · Sunnyvale .

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