Your heat pump is running, but the air from the vents feels cool — or the house just isn't climbing to temperature on a cold morning. Before you assume the system is broken, it helps to know that a heat pump behaves differently from a gas furnace, and some of what feels "wrong" is completely normal. This page separates the normal quirks from the real faults, covers what you can safely check yourself, and explains when it's time for a licensed tech.
Heat pumps are showing up in more Bay Area homes — California's electrification push and the latest Title 24 energy code have made them the default on many new installs and changeouts. Because a heat pump is your heating and your cooling, the same unit that fights inland heat in summer keeps you warm in winter — so a no-heat call is as urgent as a no-cool one.
How it usually shows up:
- The air from the vents feels cool or lukewarm and never truly hot.
- The house won't reach the set temperature on a cold morning.
- The outdoor unit is running but iced over, or the indoor air goes cold for several minutes at a time.
- "AUX" or "EM HEAT" is showing on the thermostat and the electric bill has jumped.
First, rule out normal heat-pump behavior
Two things surprise almost everyone new to a heat pump, and neither is a fault:
- Defrost cycles. In cold, damp weather the outdoor coil frosts over, so the heat pump periodically reverses to melt it. For roughly 5 to 15 minutes the indoor air blows cool and you may see steam off the outdoor unit — that's the system working correctly, and it switches back to heating on its own.
- "Warm" air is cooler than a furnace. A gas furnace pushes out air around 120–140°F; a heat pump runs gentler, delivering around 85–110°F at the vent — warmer than your body, but it can feel "not hot" against your hand. As long as the room is slowly reaching the set point, it's doing its job.
If the air is cool only briefly and then warms back up, or just isn't furnace-hot, your heat pump is probably fine. Read on if it's blowing genuinely cold air well past a defrost cycle.
Why your heat pump is really blowing cold air
When a heat pump truly won't heat, it's usually one of these:
- Reversing valve stuck in cooling. This valve flips the system between heating and cooling. If it sticks or its solenoid fails, the heat pump runs in air-conditioning mode in midwinter — steady cold air, no defrost involved.
- Low refrigerant from a leak. A heat pump moves heat with refrigerant; if it's low, there's a leak (it doesn't get "used up"). An undercharged system can't pull enough heat from cold air and often ices up. Refrigerant work is licensed-tech only (EPA 608).
- Iced-over or blocked outdoor unit. Leaves, snow, or a failed defrost cycle can encase the outdoor coil in ice, choking the heat exchange so indoor air runs cold.
- Failed defrost control board or sensor. When these fail, the outdoor coil never clears and slowly freezes solid — or the system gets stuck defrosting and blows cool air far too long.
- Auxiliary / emergency heat not engaging. On the coldest days the system leans on backup electric strip heat. If that stage or its wiring fails, the heat pump alone can't keep up and the house stays cold.
- Thermostat or aux-heat wiring fault. A miswired or failing thermostat can leave the system in the wrong mode or skip the call for backup heat.
- Dirty filter or coil. Restricted airflow cuts capacity and can freeze the indoor coil — the cheapest and most common contributing cause.
The usual fix
Our tech starts by confirming the system is calling for heat in the right mode, then checks airflow and refrigerant charge — the two things behind most weak-heat calls. From there it's usually one of a few paths: clear a dirty filter or iced coil and let it thaw, replace a failed defrost control board or sensor, repair a refrigerant leak and recharge, or free or replace a stuck reversing valve. You get a firm quote before any part goes in.
DIY vs. calling a pro — the honest version
Safe to check yourself first (free):
- Confirm it isn't just a defrost cycle. Wait 15 minutes; if the cool air warms back up, that was normal.
- Set the thermostat to HEAT — not permanently to EM HEAT or AUX. Emergency heat runs the backup strips full-time and masks a heat-pump problem.
- Change the air filter if it's dirty, and make sure vents aren't blocked.
- Clear the outdoor unit of snow, leaves, and debris, and keep a couple of feet of clearance. Never chip at ice — turn the system off and let it thaw.
Call a pro when:
- The air is still cold well beyond a 15-minute defrost cycle.
- The outdoor unit is iced solid or freezes up again right after thawing.
- You suspect a stuck reversing valve (cold air in heat mode) or low refrigerant (icing, weak heat).
- The house only stays warm on EM HEAT — a heat-pump-side fault.
Refrigerant and reversing-valve work carry high pressure and line voltage — this is where a licensed tech pays for itself.
What it costs in the Bay Area
Heat-pump repairs vary widely by the part. In our pricing, a capacitor runs about $120–$350 and a defrost control board $180–$500 — the more common fixes. A refrigerant leak repair plus recharge is roughly $180–$700 depending on the leak, and a reversing valve is the high end at $450–$900. We charge a diagnostic fee that's credited toward the repair when you approve the work, and you'll always see a flat, upfront price before we start — no surprise line items.
Get your heat pump heating again
Triton repairs heat pumps, central AC, and mini-splits across the East Bay, Tri-Valley, and Peninsula — Livermore, Pleasanton, Dublin, San Ramon, and Hayward among the inland cities where winter mornings bite hardest. Same-week (often same-day) appointments, upfront pricing, and licensed techs.
Book online or call (888) 993-5699. We'll get a tech out to find the fault and get warm air back.
Related pages
- HVAC Repair in the SF Bay Area — our full heating & cooling hub
- Heat Pump Not Cooling / Blowing Warm Air — the summer, cooling-mode version
- Heat Pump Frozen / Iced-Over Outdoor Unit — when the coil ices solid
- AC Not Cooling / Blowing Warm Air — cooling-mode diagnosis
- HVAC & Heat Pump Repair in San Ramon — Tri-Valley service area
Frequently asked questions
Why is my heat pump blowing cold air in heat mode? If it's only for 5 to 15 minutes and then warms back up, that's a normal defrost cycle. Steady cold air in heat mode usually means a reversing valve stuck in cooling, low refrigerant from a leak, or an iced-over outdoor unit — all of which need a tech.
Is it normal for heat-pump air to feel cool? Yes. A heat pump delivers air around 85–110°F, cooler than a gas furnace's 120–140°F, so it can feel lukewarm against your hand even while it's warming the room. As long as the house is slowly reaching the set temperature, that's normal heat-pump behavior.
What is a defrost cycle and how long should it last? In cold, damp weather the outdoor coil frosts over and the heat pump briefly reverses to melt it, blowing cool indoor air for about 5 to 15 minutes and sometimes steaming outside. It ends on its own and heating resumes. Cool air lasting far longer than that points to a defrost control or refrigerant problem.
Should I use emergency or auxiliary heat? Use EM HEAT only as a short-term backup — it runs expensive electric strips and bypasses the efficient heat pump. If the house only stays warm on emergency heat, the heat pump itself has a fault and needs service.
Why is my outdoor unit covered in ice? A light frost that clears during defrost is normal, but a coil encased in solid ice means the defrost cycle isn't working — often a failed defrost control board or sensor, low refrigerant, or blocked airflow. Turn the system off to let it thaw and call for service.
How much does heat-pump repair cost in the Bay Area? It depends on the part: a capacitor is about $120–$350 and a defrost control board $180–$500, a refrigerant leak repair and recharge runs roughly $180–$700, and a reversing valve is the high end at $450–$900. We credit the diagnostic fee toward the repair and give you a firm price before any work begins.