The short answer
A heat pump in Northern Virginia makes a few noises on purpose. In cold, damp weather it switches into defrost every 30 to 90 minutes: the outdoor fan stops, you hear a whoosh, and steam rolls off the top for up to about 10 minutes. A low hum and a click when it starts are normal too. Buzzing with no fan, grinding, squealing or a scream are not, and the scream means shut it off now.
What each sound means
Swipe to see all columns →
Swipe to see all columns →
| Sound | What it usually is | What to do |
|---|---|---|
| A whoosh, then steam, fan stopped | Defrost | Nothing |
| A steady low hum | The compressor running | Nothing |
| One click at start and stop | The contactor pulling in | Nothing |
| Buzzing with the fan not spinning | A capacitor, contactor or fan motor | Turn it off at the thermostat and call |
| Grinding or squealing | Motor bearings | Turn it off and call |
| Rattling | A loose panel, or ice hitting the fan | Ice on a heat pump |
| Screaming or a high whine | High pressure inside, or a failing compressor | Turn it off now and call |
| Hissing outside a defrost | A refrigerant leak | Call |
| Clicking over and over, won’t start | A relay or a capacitor | Turn it off and call |
The $67 Heating Check
We check your furnace, heat pump or boiler before winter. Through December 31. See the offer
Defrost is normal
When it’s around freezing and damp, frost builds on the outdoor coil while the heat pump pulls heat out of the air. Every so often the system reverses for a few minutes to melt it off. The fan stops so the heat stays on the coil, the reversing valve shifts with a whoosh, and the melting frost leaves as steam. People call us thinking it’s on fire. It isn’t. When it finishes, there’s a second whoosh and the fan starts again. Our posts on a heat pump covered in ice and a frozen heat pump cover when frost turns into a problem. A mini split defrosts too, and the indoor head stops blowing until it’s done: here’s mini split defrost mode.
Buzzing with no fan
If you hear a buzz or a hum and the fan on top isn’t turning, the motor is getting power and can’t start. The usual cause is the capacitor, the part that gives the motor its kick. A contactor with burned contacts or a seized fan motor do it too. Turn it off at the thermostat. Left buzzing, the compressor and motor overheat, and a capacitor is a much smaller repair than a compressor.
Grinding, squealing and screaming
Grinding or squealing from the top of the unit is the fan motor bearings wearing out. It gets louder, then the motor stops. A scream or a high whine from inside is different: it can mean pressure is too high inside the system or the compressor is failing. Shut that one off right away. Running it can turn a repair into a replacement.
What you can do safely
- Turn the system off at the thermostat, then switch to Em Heat to keep the house warm on the backup strips. Here’s how Aux and Em Heat work.
- Clear snow, leaves and anything stacked within a couple of feet of the unit.
- Look for a fan blade hitting ice, and let it melt. Don’t chip at the coil.
- Leave the service panel closed. The capacitor holds a charge after the power is off.
Here’s the full list of what not to do to your heat pump, and how a heat pump handles a Virginia winter.
Hissing and the lines
A hiss during defrost is the reversing valve and it’s fine. A steady hiss when the unit isn’t in defrost, especially with weak heat inside, can be a refrigerant leak at a fitting or the coil. That’s a call, because a heat pump low on refrigerant works harder, frosts up more and leans on the backup heat. On a ductless system, here’s how a mini split refrigerant leak shows up, and on a Daikin that won’t cool or heat, start with its own troubleshooting steps.
The outdoor unit makes the same noises in summer as an air conditioner: here’s a short video on an AC making a loud noise. Every other sound in the house is in our guide to house noises, a ductless system’s sounds are in mini split noises, and if the heat pump shows a code instead of a sound, start with error codes and warning lights.
Get ahead of it
Our heating check is $67 per system, through December 31: furnace, heat pump or boiler. On a heat pump we test the capacitor, the contactor, the defrost controls and the backup heat. More on heat pump repair.
Book it
A repair visit starts with a flat $99 diagnostic, or $250 after hours, and you get the price of the fix before we touch anything. Call (703) 997-9757, day or night, or book online from goswiftpro.com/cookiesoffer by November 30 and a box of warm MOLTN cookies comes with the heating check. Every current deal is on our offers page. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
Why is my heat pump making a whooshing noise?
It’s switching into or out of defrost. In cold, damp weather it melts the frost off the outdoor coil every 30 to 90 minutes. The fan stops, you hear a whoosh, and steam comes off the top. That’s normal.
Is it normal for a heat pump to make noise in winter?
Some, yes: the defrost whoosh, steam, a steady hum and a click at start. Buzzing with no fan, grinding, squealing or a scream are not normal.
Why is my heat pump buzzing?
If the fan isn’t turning, the motor has power and can’t start, usually because of a bad capacitor. Turn it off at the thermostat and call, so the motor and compressor don’t overheat.
What should I do if my heat pump is screaming?
Turn it off at the thermostat right away and switch to Em Heat. A scream can mean high pressure inside the system or a failing compressor.
