Heat Pump Not Heating in Portola Valley

Heat Pump Not Heating in Portola Valley

Portola Valley sits in wooded hills off Alpine Road and Portola Road, and the shaded, tree-covered lots stay cooler and damper than open ground. That matters for heat pumps, because a coil placed on a shaded side of a property frosts over more readily on a cool, humid morning. A heat pump handles that normally with a defrost cycle, but when the defrost control fails, the coil ices over, the outdoor unit loses its ability to pull heat from outside air, and the house stops warming.

These are large custom homes on wooded acreage, and some run more than one independent system across the main house and an addition or separate wing. So a no-heat call here is usually one of two things: a single system failing on a larger property, or an iced coil on a unit set into a cold, shaded pocket of the lot. The mild climate here means the equipment is never actually pushed past its range, which is why these calls almost always trace to one specific part rather than a system that can't keep up.

On the outer roads with well and septic setups, equipment placement sometimes got worked around those systems, and that placement is part of what we look at when diagnosing where the ice or the fault started. The diagnostic fee credits toward the repair on most jobs.

Common causes

Failed defrost control on a shaded coil. On a cool, damp Portola Valley morning, the outdoor coil can frost, and the defrost board is supposed to briefly reverse the cycle to melt it. When that board or its coil sensor fails, ice keeps building, the coil can't pull heat from outside air, and heating output collapses. We confirm the defrost cycle actually initiates and the sensor reads correctly, then replace the board if it isn't commanding defrost.

Outdoor coil iced over. If we arrive to a coil packed in ice, a defrost fault is the usual root cause, but a low refrigerant charge or a stuck fan motor can ice a coil too. We clear the ice, then find out why it formed instead of just thawing it and moving on. Skipping that step just means a callback within the week.

Stuck reversing valve. The reversing valve is what flips the system into heating mode. A failed solenoid or a valve stuck mid-stroke leaves the unit running in cooling or stalled entirely, so it blows unheated air on that system while others on the property stay fine. We meter the solenoid and check line temperatures to verify the valve truly shifted before any replacement.

Low refrigerant charge. A heat pump running low on refrigerant loses heating capacity first and can also frost the outdoor coil in the process. We find the leak with electronic detection instead of topping off, repair it, then weigh in the correct charge. On properties with more than one system, usually only the affected unit is low, so we isolate that one.

Control board or zone fault on one system. On a property with multiple systems or zoning across a larger floor plan, a drifting control board or a damper stuck closed can drop heat to one wing while the rest stays warm. We read the board status and test damper actuators to find the system that actually lost the call instead of guessing at the equipment.

How we diagnose it

• The outdoor unit gets looked at first for ice on the coil, which points straight at defrost or charge.
• Checking the defrost board's ability to start a cycle and the coil sensor's accuracy comes first.
• Line temperature readings confirm whether the reversing valve truly shifted into heating mode.
• We check refrigerant pressures against the outdoor temperature to catch a low charge that's frosting the coil.
• On properties with more than one system, we map which unit or wing is affected before touching the equipment.

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

Heat Pump Not Heating in Portola Valley: common questions

Nearby and related

Heat Pump Not Heating near Portola Valley: Woodside · Menlo Park · Los Altos Hills .

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