Heat Pump Not Heating or Cooling? Here’s What to Check

If your heat pump isn’t heating or cooling, you’re in very familiar homeowner territory. I’ve had that moment where you bump the thermostat a few degrees, wait… and nothing changes — and suddenly you’re doing mental math on “how bad is this going to be?” The good news: a lot of heat pump problems come from simple, safe causes you can check without opening the unit or messing with wiring.

Quick triage tip: Before you do anything else, notice what’s happening. Is the thermostat screen on? Is the indoor fan running but the air feels “wrong”? Is the outdoor unit quiet? Those little clues usually point you to the right section below.

If you want a simple “start here” path for home fixes, this page is a good bookmark: Start here: the simplest path to the right fix.

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1) Check the Thermostat Settings (the “it happens to the best of us” fix)

Start with the simplest step. I’m not kidding — I’ve seen a system “broken” because it was accidentally set to the wrong mode, or the fan was set to On so it was blowing room-temperature air between heating/cooling cycles. Using Auto is generally the better default for heat pump performance.

What to verify:

Thermostat is set to Heat or Cool (not the opposite).
Temperature is set far enough away from the current room temp to trigger a call (a few degrees, not just one).
Fan is set to Auto, not On.

If your AC also struggles to cool, you may find this guide helpful:

AC Not Cooling? Here’s What to Check

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2) Make Sure the Outdoor Unit Isn’t Blocked (airflow = everything)

Heat pumps rely on steady airflow. If the outdoor unit can’t “breathe,” performance drops fast — and sometimes the system will struggle so much it feels like it’s not doing anything at all.

What to look for:

Leaves, grass, or debris packed around the unit
Snow or ice buildup (in winter)
Objects stored too close (bins, lumber, patio furniture, etc.)

My rule of thumb: keep a clear “breathing zone” around the unit. If you can stand next to it without bumping into shrubs or stuff, you’re usually in a safer range. (And yes — I’ve seen a heat pump boxed in by a “quick” storage pile that slowly became permanent.)

For more HVAC topics, browse: HVAC or jump to the Category Index.

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3) Replace or Clean the Air Filter (the most common “why is it weak?” cause)

A clogged filter restricts airflow and can make a heat pump feel underpowered — or like it’s running forever without catching up. If you do one maintenance habit consistently, make it this one: clean or replace filters on a regular schedule (many systems do well with checking monthly and changing at least every few months, depending on dust/pets/allergies).

Signs of a dirty filter:

Weak airflow from vents
Heat pump seems to run constantly
Uneven temperatures from room to room

If your furnace also struggles with airflow, see:

Furnace Not Heating? Here’s What to Check

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4) Check the Circuit Breaker (and take repeat trips seriously)

If the heat pump loses power, it won’t heat or cool — and sometimes only part of the system loses power (indoor runs, outdoor doesn’t). Check your panel for a breaker labeled “Heat Pump,” “Outdoor Unit,” or similar.

What to check:

Breaker labeled “Heat Pump” or “Outdoor Unit”
Reset if tripped (flip fully OFF, then back ON)

Important: If the breaker trips again after you reset it, stop. That’s not a “keep trying” situation — it’s a sign the system needs professional service.

More electrical safety + troubleshooting lives here: Electrical and Home Safety.

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5) Inspect the Outdoor Unit for Ice (Winter) — and know what’s “normal”

Heat pumps can frost up in cold weather — and many systems handle it automatically with a defrost cycle. During defrost, it’s normal for the unit to temporarily change operation to melt frost off the outdoor coil, and you may even see steam/vapor outside.

What to do:

Check for ice buildup that blocks airflow
Give the system time to run a defrost cycle if frosting is light/temporary
Clear snow around the base so the unit can drain and breathe

If the entire unit is encased in ice (not just light frost that clears), that’s a “call a technician” moment.

Bonus “human” tip: if you’re troubleshooting during a serious cold snap or heat wave, it’s worth reviewing emergency readiness basics too: Ready.gov: Extreme Heat preparedness.

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6) Check for Dirty Coils (usually a pro job)

Dirty coils can reduce efficiency and heating/cooling output. If airflow and settings are right but performance is still weak (and bills are creeping up), coils may be part of the story. In most cases, coil cleaning is a professional job — especially if you’re talking about the indoor coil.

Signs:

Heat pump runs constantly
Weak heating or cooling
Higher energy bills than normal

You can safely do the “outside only” basics (remove debris around the cabinet), but if you suspect coil cleaning beyond that, I’d keep it in the pro lane.

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7) Listen for Unusual Noises (your early warning system)

Strange sounds can indicate mechanical issues. If you hear something new and unsettling, don’t ignore it — I’ve learned the hard way that “maybe it’ll go away” is rarely the winning strategy with HVAC.

Warning sounds:

Grinding
Buzzing
Rattling
High‑pitched squealing

Turn off the system and call a technician if you hear these noises.

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8) Check the Reversing Valve (Professional Diagnosis)

The reversing valve is what allows a heat pump to switch between heating and cooling. If it fails, a heat pump may get “stuck” in one mode (only heat or only cool), or struggle to do either properly — and this is firmly a professional repair.

If it fails, the heat pump may:

Only heat
Only cool
Do neither (or do both poorly)

This requires professional repair.

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When to Call an HVAC Technician (my “stop here” list)

Heat pumps are complex — and there’s a point where it’s smarter (and safer) to stop DIY troubleshooting.

Call a professional if:

The heat pump won’t switch modes (stuck heating or cooling)
Airflow is extremely weak even after a filter change
The outdoor unit is frozen solid (not just light frost)
The breaker keeps tripping
You hear grinding, buzzing, or other harsh noises
The system short‑cycles (turns on/off rapidly)

If you want to read more about good operation and maintenance habits (and what a tech typically checks during annual service), this is a solid reference: DOE: Operating and Maintaining Your Heat Pump.

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Prevention Tips (small habits, big payoff)

Replace air filters regularly
Keep the outdoor unit clear of debris and clutter
Clean vents and registers (especially returns)
Schedule annual HVAC maintenance
Keep shrubs trimmed around the unit

These habits improve performance and extend system life — and they reduce the odds you’ll be troubleshooting on the hottest or coldest day of the year.

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⭐ Related Guides & External Resources

Related Guides

External Resources