Heat Pump Not Heating? Safe Checks and Common Causes

Quick answer

A heat pump that isn't heating often has a thermostat setting problem, a dirty filter, a blocked outdoor unit, or an issue a technician needs to find, like a failed part or low refrigerant. Check settings, filter, breakers, and the outdoor unit first. If the air from vents stays cool, have it checked.

Key facts

Normal	Air feels warm, not hot; long run times on cold days
Also normal	Short defrost cycles with steam from the outdoor unit
Not normal	Cool air from vents for a long stretch, or an outdoor unit that won't run
Safe checks	6: settings, batteries, filter, breakers, outdoor unit, vents
Don't	Chip ice or open the outdoor unit

Why is my heat pump not heating the house?

The most common reasons are simple ones: a thermostat setting, a dirty filter, or an outdoor unit that can't breathe. Others need a technician, like a failed capacitor or fan motor, a stuck reversing valve, or low refrigerant from a leak.

A heat pump moves heat from the outdoor air into your home. When any part of that loop slows down, the house can feel cool even though the system keeps running.

Is my heat pump broken, or is this normal?

Some things that feel wrong are normal. Heat pump air usually feels warm, not hot like a gas furnace. In cold weather, it may run for long stretches to keep up.

ENERGY STAR advises picking a comfortable temperature and leaving it there, because heat pumps don't save energy by turning down when you're away or asleep. A big setback can leave the heat pump working hard to catch up, and may bring on backup heat.

Long run times on cold days: normal
A short defrost cycle, with steam or a whoosh from the outdoor unit: normal
Air from the vents that feels cool for a long time: not normal
Outdoor unit silent while the indoor fan runs: not normal
A thick block of ice that doesn't clear: not normal

Not sure what's wrong yet?

Start with the safe checks. Many problems are a setting, a breaker, or a filter.

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What can I check on a heat pump that isn't heating?

These 6 checks are safe for any homeowner. Anything inside the outdoor unit or indoor cabinet is a job for a technician.

1Set the thermostat to Heat, not Auto or Cool. ENERGY STAR suggests avoiding Auto mode on heat pumps.
2Replace the thermostat batteries if the screen is blank.
3Check the filter at the indoor unit and replace it if it's dirty.
4Check the breakers for both the indoor and outdoor units. Reset a tripped breaker once. If it trips again, stop.
5Look at the outdoor unit. Clear leaves, snow, and stored items away from it so air can flow. Don't chip at ice or open the panels.
6Walk the house and make sure supply vents and return grilles are open and not blocked by furniture or rugs.

What usually causes a heat pump to stop heating?

Under EPA rules, technicians who handle refrigerant must be certified. So anything involving refrigerant is never a homeowner job.

What you notice	Common cause	Can you check it?
Cool air, outdoor unit not running	Tripped breaker, failed capacitor, or failed contactor	Breaker, yes. Parts, no.
Outdoor unit hums, fan not spinning	Fan motor or capacitor failure	No. Leave it for a technician.
Weak airflow from vents	Dirty filter, blocked returns, or a blower problem	Filter and returns, yes.
Cool air while set to Heat	Reversing valve or control problem	No.
Some heat, but never enough	Low refrigerant from a leak, or dirty coils	No. Refrigerant work needs a certified technician.
Aux or emergency heat shows often	The heat pump isn't keeping up, or a setting	You can check the setting.

When should I call about a heat pump that won't heat?

Call when the safe checks are done and the air is still cool, or when the outdoor unit won't run at all.

If the house is getting too cold, you can switch the thermostat to emergency heat to use your backup heat, if your system has it. It often costs more to run, so treat it as a short-term fix. Our aux and emergency heat guide explains the difference.

A breaker trips again after one reset.
The outdoor fan isn't turning while the unit hums.
The unit is iced solid and stays that way.
You hear grinding, screeching, or loud buzzing.

What will a technician check on my heat pump?

A technician tests the heat pump in heating mode and works through the parts that move heat, starting with power and airflow.

Power, capacitor, and contactor at the outdoor unit
Outdoor fan motor and compressor
Reversing valve and defrost controls
Refrigerant pressures, and signs of a leak
Filter, blower, and coils

How does repair-first work for a heat pump?

Most heat pump heating problems are parts, airflow, or refrigerant leaks that can be repaired. We fix what can be fixed — and tell you straight when it can't.

You'll hear what's wrong and the price before any work starts, and nothing happens until you say yes. If the heat pump is near the end of its life, we'll explain why and show you both options.

Common questions

Why does my heat pump blow lukewarm air?

Heat pump air often feels lukewarm because it's warmer than the room but cooler than your skin. That's normal while the house slowly warms up. If the house never reaches the set temperature, check further.

Should I turn my heat pump down at night?

Usually not, because ENERGY STAR says heat pumps don't save energy by turning down when you're away or asleep. It suggests picking a comfortable temperature and leaving it there. Big setbacks can make the system work hard to catch up.

Is it OK to use emergency heat?

Yes, for a short time while you wait for a repair. Emergency heat uses your backup heat instead of the heat pump, and it often costs more to run. Switch back to normal heat once the heat pump is fixed.

Why is my heat pump running all the time?

Long run times are normal in cold weather, since a heat pump puts out steady, gentle heat. It's a concern if the house still can't reach the set temperature, or bills jump without a change in weather. Start with the filter and the outdoor unit.

Does a heat pump need refrigerant added every year?

No, a heat pump shouldn't need refrigerant added every year, because it's a sealed system. If it's low, there's a leak, and the leak is what needs fixing. Refrigerant work is for certified technicians.

Why won't my outdoor unit run in heat mode?

Often it's a tripped breaker, a failed capacitor, or a contactor that isn't closing. You can check the breaker and reset it once. Parts inside the unit carry high voltage, so leave them for a technician.