Every winter we get the same call, usually around 7 a.m. from someone standing in their driveway in a bathrobe. The outdoor unit is fogging like a kettle, the top of it is wet, there's frost on the lawn but not on the unit, and the system sounds different than it did five minutes ago.
Nine times out of ten, that's a heat pump working correctly. The tenth time is a real repair. Here's how to tell which one you're looking at without guessing.
What the defrost cycle actually is
A heat pump in heating mode pulls heat out of outdoor air. To do that, the outdoor coil has to be colder than the air around it. When the outdoor air is between roughly 30°F and 45°F and damp — which describes most of a Puget Sound winter — moisture in the air condenses on that cold coil and freezes. Frost on a coil is insulation. Insulation on a heat exchanger kills capacity fast.
So the system fixes itself. It briefly flips the reversing valve into cooling mode, sends hot refrigerant out to the outdoor coil, shuts off the outdoor fan, and melts the frost off. Indoors, a small amount of backup electric heat usually kicks on for those few minutes so you don't feel a cold draft. Then it flips back and goes on heating your house.
That's the whole event. The steam is melted frost leaving as vapor. The unit being hot to the touch is intentional. The whoosh or soft thud when it starts and finishes is the reversing valve changing position.
If you want the bigger picture on why this climate is actually easy on heat pumps, we wrote that up separately in Do Heat Pumps Work in Washington Winters?. Short version: yes, and defrost is part of why.
The normal-defrost checklist
Stand there for 15 minutes with a phone timer. Normal looks like this:
- Frequency: roughly every 30 to 90 minutes in cold damp weather. Less often in dry cold.
- Duration: 5 to 15 minutes, then it ends on its own.
- Outdoor fan: off during defrost, back on when it finishes.
- Steam: visible vapor off the top and sides of the coil, sometimes a lot of it.
- Water: a puddle or a wet pad under the unit afterward. That's melted frost draining.
- Sound: one soft thud or hiss at the start, one at the end.
- Indoor air: slightly cooler for a few minutes, not cold.
- After: the coil is clear, the unit resumes normal heating, and the house recovers temperature.
If all of that describes your unit, nothing is wrong. Don't turn it off. Don't switch to emergency heat — that's the most expensive way to heat a house in Washington, and running it out of worry costs real money on your bill.
What isn't normal
Here's the same event when something is actually broken.
| What you see | What it usually means |
|---|---|
| What you seeSolid ice covering the whole coil for hours | What it usually meansDefrost isn't running, or it can't keep up |
| What you seeIce rebuilds within minutes of a defrost ending | What it usually meansLow refrigerant charge or a restricted coil |
| What you seeDefrost every 10 to 15 minutes, all day | What it usually meansFailed defrost sensor, board, or thermostat wiring fault |
| What you seeUnit never defrosts, frost just grows | What it usually meansFailed defrost control, sensor, or reversing valve |
| What you seeIce only on the top of the unit | What it usually meansA gutter, downspout, or roof edge dripping onto it |
| What you seeLoud screech, grind, or repeated hard clunking | What it usually meansFan motor or compressor issue — shut it down |
| What you seeIndoor air cold for 10+ minutes at a time | What it usually meansBackup heat not engaging during defrost |
| What you seeRuns constantly, house never gets warm | What it usually meansSee our heat pump not heating guide first |
Free things to check before you call anyone
We'd rather you fix it for nothing than pay us for a service call you didn't need.
- Thermostat is on HEAT, not EM HEAT. Emergency heat locks out the compressor entirely.
- Clear 18 to 24 inches around the unit. Leaves, blackberry, bark, a stack of firewood, a tarp somebody threw over it in October.
- Look up. A dripping gutter or a roofline shedding water onto the top of the unit will re-ice a coil faster than any defrost cycle can clear it. This is genuinely one of the most common causes we find in Federal Way, Kent and Puyallup, where a lot of 1970s–90s homes have the condenser tucked under an eave.
- Change the filter. Restricted indoor airflow drops coil temperature and drives icing.
- Make sure the unit isn't sitting in a low spot that pools water. Frozen standing water around the base holds frost against the coil.
If all five check out and the ice is still winning, it's a real repair.
What defrost repairs cost
Defrost problems are usually a component, not a catastrophe. Heat pump repair in standard Puget Sound markets runs $150 to $1,500, $175 to $1,800 in affluent markets like Seattle or Maple Valley, and $200 to $2,000 in luxury markets like Bellevue and Gig Harbor. A defrost thermostat, sensor or relay sits at the low end. A control board sits in the middle. A condenser fan motor or a refrigerant leak that requires recovery, repair and recharge sits at the top.
Our repair process is boring on purpose: a technician diagnoses it, gives you the price before touching anything, and fixes it the same day when the part is on the truck. If it needs ordering, we schedule the return visit. Details are on the heat pump repair page.
When a defrost problem is really a replacement conversation
We'll tell you straight when the math stops working. The honest triggers:
- The system is 12 to 15+ years old and facing a four-figure repair.
- It still runs R-22 refrigerant, which is expensive and getting harder to source every year.
- Repeat icing that's traced to a leaking or corroded coil — common on salt-air properties in Des Moines, Burien, Steilacoom and Gig Harbor.
- The repair cost is more than half the cost of a new system.
Heat pump replacement runs $10,000 to $16,000 in standard markets and $11,500 to $19,200 in affluent and luxury markets, and every Varsity install carries a 10-year parts and labor warranty. Most are done in one day.
On rebates, frame it the way it actually works: local utility rebate money may be available toward a qualifying heat pump when it replaces an existing electric or fossil-fuel system, and what it pays depends on what you're replacing and what you install. Programs change, so we confirm your current eligibility and handle the paperwork. Two facts worth knowing before you sign anything: the federal 25C tax credit ended December 31, 2025, and utility rebate programs pay only through their own contractor networks, with rules that move around. Ask any company bidding your job whether they have checked the current requirements, because otherwise the rebate quietly evaporates at the end.
Also worth checking: rebates follow the meter, not the county. If Tacoma Power, Peninsula Light, Seattle City Light or a Parkland-area mutual bills your electricity, you're in that utility's own program, not the one advertised everywhere else. We sort that out by address.
What we do on a defrost call
A technician verifies the defrost initiation and termination temperatures, checks the sensor and board, confirms the reversing valve actually shifts, measures refrigerant charge and superheat, inspects the coil for restriction and corrosion, checks outdoor fan operation, and looks at what's physically around and above the unit. That last one solves more cases than people expect.
If the answer is "nothing's wrong, that's normal steam," you'll hear that too. Our reviews mention honesty about repair costs more than anything else, and that's not an accident.
Get a real number
If your unit is iced over right now, call (253) 785-4622. Service hours are Monday through Friday, 8 to 6, with same-week scheduling. If you're already past the repair question and pricing a replacement, the fastest path is our instant estimate tool — seven questions, Good/Better/Best starting prices in about 60 seconds — or request a free in-home estimate and we'll run a real load calculation before quoting anything. If you want to compare a full system swap while you're at it, start on the heat pump installation page.
Steam in the driveway on a cold morning is usually the sign of a heat pump doing its job. A block of ice at noon is not. Now you know which one you've got.