The short answer
When a York heat pump isn’t heating in Northern Virginia, it’s often in defrost: the outdoor fan stops, the coil melts its frost for a few minutes, and the backup heat runs meanwhile. York’s own manual says frost can build up unevenly and that defrost can start before the coil is fully covered. That’s normal. What isn’t normal: an outdoor unit that never runs, a coil that stays a solid block of ice, or air at the vents that stays cool for hours. Check the thermostat, both breakers, the filter and the outdoor coil, then call.
How York’s defrost works
From York’s YH4 heat pump install manual (the single-stage YH4 and its sister models): the control watches the coil temperature. Once the coil has been cold enough for 4.5 minutes straight, or after 6 hours of compressor run time, it starts a defrost. The heat pump switches to cooling with the outdoor fan off, so the hot refrigerant melts the frost, and it turns on the backup heat so the house doesn’t get a blast of cold air. When the coil warms up, defrost ends, the fan restarts and heating picks back up. After each defrost the control waits at least 40 minutes before it can start another.
How long a defrost can run depends on the model: up to 14 minutes on the YH4, up to 12 on the variable-speed YH9. A few minutes is typical.
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Other normal things
- Uneven frost. The manual says frost may build up unevenly on the coil. A frosty bottom and a clear top is fine.
- Vapor and water. Melting frost runs off the coil and can steam. The manual warns it will freeze, which is why the unit should sit where that water drains away.
- Warm, not hot, air. Heat pump air feels warm rather than hot, with longer cycles than a furnace.
Check these first
- The thermostat. Heat mode, a few degrees warmer than the room.
- Both breakers. One for the outdoor unit, one for the air handler, plus the disconnect box beside the outdoor unit.
- The filter and the vents. A clogged filter or closed vents cut the heat.
- The outdoor coil. Brush off snow and leaves by hand. Don’t chip at ice; the fins bend and the tubes puncture.
- One power cycle. Set the thermostat to off. Turn off the breaker or the switch for the equipment, wait about five minutes, turn it back on and set the thermostat back. Do it once. York’s outdoor control clears a pressure switch soft lockout when the thermostat call drops and comes back.
Read the light on the outdoor board
The outdoor control has an LED that blinks a fault count. You’ll need the service panel off to see it, so it’s often easier to let a tech read it. A slow on and off blink with no call is normal, steady on means the compressor is running. These are the fault counts from the YH4 manual:
Swipe to see all columns →
Swipe to see all columns →
| Flashes | What it means |
|---|---|
| 2 | High pressure switch opened |
| 3 | High pressure switch lockout |
| 4 | High pressure switch lockout during a defrost |
| 5 | Low pressure switch lockout |
| 8 | Coil temperature sensor fault |
| 9 | Outdoor air temperature sensor fault |
| 11 | The thermostat is sending heat and cool signals at the same time |
Communicating York heat pumps such as the YZT have a two-character display on the outdoor board instead. Running normally, it shows a status: dd, td or Fd for a defrost, A1 or A2 when the backup heat is on, E1 or E2 for emergency heat. A number is a fault. These are the ones behind a heat pump that stops heating, from the YZT install guide:
Swipe to see all columns →
Swipe to see all columns →
| Code | What it means |
|---|---|
| 01 | High pressure switch open, often a dirty outdoor coil or an outdoor fan that stopped |
| 02 | High pressure trips again: 2 in 6 hours is a soft lockout, 4 soft lockouts in 12 hours a hard lockout |
| 03 | The same high pressure trips, during a defrost |
| 04 | Low pressure switch open more than 5 seconds, often low refrigerant or an iced coil |
| 09 | Outdoor temperature sensor fault |
The usual causes, one at a time
The outdoor unit doesn’t run
What you notice: The air handler blows, the air is cool or slightly warm, and outside it’s quiet.
What causes it: No power outdoors (breaker or disconnect), a failed capacitor or contactor, or a pressure switch lockout: a second high pressure trip within 6 hours is a soft lockout.
What you can do: Check the outdoor breaker and disconnect, then one power cycle.
When to call us: If it doesn’t start, or starts and stops again.
It’s frozen solid
What you notice: A solid block of ice on the coil that doesn’t clear through the day, or ice building up from the base.
What causes it: Defrost isn’t working (the coil sensor, 8 flashes, or the outdoor air sensor, 9 flashes), the reversing valve, or meltwater that can’t drain and refreezes under the unit.
What you can do: Clear loose snow, fix any gutter dripping on the unit, and switch to emergency heat if the house is getting cold.
When to call us: Same day. Our York repair page prices the defrost board.
Low pressure lockout
What you notice: It ran, then stopped. The outdoor board flashes 5.
What causes it: Usually low refrigerant from a leak, sometimes a dirty filter or coil starving the system of airflow.
What you can do: Change the filter. One power cycle.
When to call us: If it comes back. A leak gets found and fixed, not just topped off.
Backup heat isn’t working
What you notice: Normal days are fine, but on the coldest nights the house slides, and during a defrost the air turns cold.
What causes it: The heat strips in the air handler aren’t running: a failed strip, its limit or its breaker. York’s control calls the backup heat during every defrost, so a dead strip shows up there first.
What you can do: Check the air handler’s breakers; the strips often have their own.
When to call us: If the breakers are on and there’s still no backup heat.
Emergency heat
Emergency heat turns the outdoor unit off and heats the house with the strips alone. Use it when the heat pump is frozen solid or won’t run, until a tech gets there. It costs more to run, so don’t leave it on once the heat pump is fixed. Our aux heat vs emergency heat guide has the details.
What the visit looks like
The tech reads the outdoor board’s fault count, checks power at both units, tests the capacitor and contactor, measures refrigerant pressures, checks the coil and outdoor air sensors, forces a defrost to watch it start and end, and checks the backup heat. You get the cause and the price before any part goes in.
Other brands: Trane heat pump not heating and American Standard heat pump not heating. Ice and winter: heat pump covered in ice and heat pumps in a Virginia winter. A York gas furnace instead: York furnace not turning on. Every brand is in our error codes and warning lights guide, and our York repair page and heat pump repair page have what we fix and what it costs.
The system we put in first
Built to take a beating. Put in by our crew.
Heat lamps, snow and rain on one outdoor unit: that’s Trane’s own film. We’re a Trane Comfort Specialist, on Trane’s own dealer locator, and when you pick a Trane, our crew puts it in.
Films: Trane’s own.
Book a York repair
Call (703) 997-9757 or book online. A diagnostic visit is $99, and the tech reads the code, finds the part that set it and gives you the price before any work starts. We answer day or night. Our heating check is $67 per system, through December 31: furnace, heat pump or boiler. If someone already quoted you a new system, our free second opinion looks at it first. 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 York heat pump not heating?
It may be in defrost, which is normal and lasts a few minutes. If it isn’t, check the thermostat, the breakers for both units, the filter and the outdoor coil. An outdoor unit that won’t run or a coil frozen solid needs a call.
Is uneven frost on my York heat pump normal?
Yes. York’s manual says frost may build up unevenly and the control may defrost before the coil is fully covered. A solid block of ice that stays is not normal.
How often does a York heat pump defrost?
When the coil has been cold enough for 4.5 minutes straight, or after 6 hours of compressor run time, with at least 40 minutes between defrosts on the YH4.
Why does my York heat pump blow cold air during defrost?
York’s control turns on the backup heat during defrost to cover the cold air. If the air turns cold every defrost, the heat strips or their breaker may have failed.
Should I use emergency heat on my York heat pump?
Only when the heat pump is frozen solid or won’t run, until it’s fixed. It heats with the electric strips alone, which costs more to run.
