TL:DR: Your heat pump switches to emergency heat when the thermostat has manually cut off the compressor — usually because someone flipped the “Emergency Heat” switch, or because a fault (tripped breaker, refrigerant leak, failed compressor, stuck ice) forced it into backup-only operation. Emergency heat is different from auxiliary heat, which kicks in automatically alongside the heat pump on cold days. Emergency heat runs the backup electric strips alone, at roughly 2 to 3 times the cost per hour. If it’s on and you didn’t set it, or it won’t turn off once temperatures rise above the low 30s°F, that’s a real fault and needs a technician — not just patience.
Quick Check: Is This Normal Right Now?
Before reading further, run these three checks — they resolve most “why is my heat pump on emergency heat” questions in under two minutes:
1: Did a person switch it on?Look at the thermostat mode setting. If it reads “Emergency Heat” or “EM Heat” and you (or someone else in the house) manually selected it, that’s expected — it’s working exactly as designed until a technician arrives.
2: Is it below freezing outside, or is the outdoor unit iced over?Brief auxiliary or emergency heat use during a hard freeze, or a normal 5–15 minute defrost cycle, is expected. This is different from emergency heat staying on for hou
3: Has it been running non-stop for more than 1–2 hours in mild weather (above 40°F)?If yes, and nobody manually activated it, this is the clearest sign of an actual heat pump fault — skip to the causes section below.
Emergency Heat vs. Auxiliary Heat: What’s the Difference?
This is the single most confused pair of terms on a heat pump thermostat, and manufacturers are specific about the distinction:
|
Auxiliary Heat |
Emergency Heat |
|
| How it activates |
Automatically, by the thermostat |
Manually, by a person (or triggered when the system can’t verify the heat pump is running) |
| Runs with the heat pump? |
Yes — supplements it |
No — heat pump is shut off entirely |
| Typical trigger |
Outdoor temp below ~35–40°F, a defrost cycle, or a 3–4°F setpoint jump |
Heat pump failure, refrigerant issue, electrical fault, or a manual switch flip |
| Cost vs. normal heat pump operation |
Higher, but temporary and proportional |
2–3x higher, and open-ended if left on |
| Normal in Northern Virginia winters? |
Yes, on cold nights (20s°F and below) |
Only briefly, and only if intentionally activated |
According to Trane’s residential support documentation, auxiliary heat is triggered automatically by the thermostat — usually when outdoor temperatures drop below about 40°F, when the heat pump enters a defrost cycle, or when you raise the setpoint by more than 3 to 4 degrees at once. In all of those cases, the heat pump keeps running; the strips just add extra heat on top of it.
Emergency heat is a separate, manually-selected mode. Lennox’s support documentation describes it plainly: emergency heat uses the second-stage supplemental heat by itself, without the heat pump running at all. When you or a previous occupant flips the thermostat to “Emergency Heat,” the system assumes the heat pump has failed and shuts the compressor down on purpose, relying entirely on the electric strips (or furnace, in a dual-fuel system) to carry the entire heating load.
The distinction that matters: auxiliary heat is a helper, emergency heat is a replacement.
What Does “Emergency Heat” Mean on My Thermostat?
If your thermostat display shows “Emergency Heat,” “EM Heat,” or a red “E” icon, it means the system has stopped using the outdoor heat pump unit entirely and is heating your home only with the backup electric strips (or, on a dual-fuel system, the gas furnace). This mode has to be manually turned on — it will not turn off by itself even after the underlying problem is fixed. You have to switch the thermostat back to “Heat” or “Auto” once you know the heat pump is working again.
Why Is My Heat Pump on Emergency Heat? Signs Something’s Wrong
● The thermostat display reads “EMERGENCY HEAT” or “EM HEAT” while outdoor temperatures are still in the 40s or 50s°F — well above where any backup heat should be needed.
● Nobody in the household flipped the emergency heat switch, yet the system is running on it anyway.
● Your electric bill has jumped noticeably compared to the same week last winter, with no corresponding cold snap.
● The outdoor unit’s fan isn’t spinning, or the compressor is silent, while the indoor air handler keeps blowing warm air.
● The system stays in emergency heat for more than an hour or two straight, even in normal Northern Virginia winter weather (mid-20s to low-30s°F).
● You hear the outdoor unit short-cycling — turning on and shutting off within seconds — before the system falls back to emergency heat.
Every Cause of a Heat Pump Stuck on Emergency Heat
1: Someone (or a previous occupant) manually switched the thermostat to Emergency Heat. This is the single most common cause on service calls. If you just moved in, inherited a system from a tenant, or a family member “fixed” a cold house by flipping the setting, the heat pump may be sitting idle even though nothing is actually broken.
2: A tripped breaker or blown fuse at the outdoor unit. If the heat pump’s outdoor disconnect has no power, some thermostats and control boards default to emergency heat automatically so the house doesn’t go cold while you sort out the electrical issue.
3: A refrigerant leak or critically low refrigerant charge. Without enough refrigerant, the heat pump can’t move heat efficiently or at all. A control board that detects abnormal pressures or a failed compressor start can lock out the compressor and fall back to emergency/backup heat.
4: A failed or frozen outdoor compressor. If the compressor won’t start — due to a bad capacitor, contactor, or internal failure — the heat pump physically cannot produce heat, and the system relies on the backup strips or furnace until it’s repaired.
5: Ice buildup on the outdoor coil that isn’t clearing during defrost. A normal defrost cycle briefly uses auxiliary heat and resolves itself in 5–15 minutes. If the coil stays iced over because the defrost control board, reversing valve, or outdoor sensor has failed, the system can get stuck relying on backup heat far longer than normal. See the defrost section below if this is your situation.
6: A dirty air filter or blocked outdoor unit restricting airflow. Reduced airflow across the indoor or outdoor coil can trigger pressure faults or force the system to lean harder on backup heat to compensate.
7: A miswired or failed thermostat, or outdated smart thermostat firmware. Incorrect wiring (especially after a DIY thermostat swap) or a failed thermostat control board can send the wrong signal, activating emergency heat mode when it shouldn’t, or preventing the system from switching back to normal operation.
8: Reversing valve failure. The reversing valve is what lets a heat pump switch between heating and cooling. If it sticks, the heat pump may be unable to deliver heat at all, even though the outdoor unit is running, pushing the system onto backup heat by default.
9: A faulty outdoor temperature sensor or control board. A sensor that misreads outdoor conditions can cause the system to assume the heat pump can’t handle the load and default to backup heat even in mild weather.
Is Your Heat Pump Stuck in a Defrost Cycle Instead?
Sometimes what looks like an emergency heat problem is actually a stuck defrost cycle. A normal defrost cycle reverses the heat pump briefly to melt frost off the outdoor coil, uses auxiliary heat to keep the house warm during that window, and finishes in 5 to 15 minutes. It becomes a real problem when the ice never clears — usually because of a failed defrost control board, a bad outdoor temperature sensor, a jammed reversing valve, or low refrigerant that leaves the system without enough heat to melt the coil. If your outdoor unit has been visibly iced over for longer than 15–20 minutes, or the system seems to cycle into “defrost” repeatedly without ever fully clearing, that’s a defrost-system fault, not routine operation, and it needs a technician.
Heat Pump Emergency Heat Won’t Turn Off? Do This First
Emergency heat does not turn itself off — it stays active until someone manually switches the thermostat back, even after the original problem is resolved. If yours won’t turn off or seems to keep reactivating, work through these steps in order:
1: Confirm the thermostat mode. Set it back to “Heat” or “Auto” (not “Emergency Heat”) and see if the system responds normally within a few minutes.
2: Check the breaker panel. Reset any tripped breakers connected to the outdoor heat pump unit or indoor air handler.
3: Inspect the outdoor unit. With power off, clear away snow, leaves, or debris, and keep at least two feet of clearance on all sides. Light frost is normal; a thick coat of ice that isn’t melting after an hour is not.
4: Replace the air filter if it’s dirty. A clogged filter restricts airflow and can force the system into a fault state.
5: Make gradual thermostat adjustments. Raise the setpoint by only 1–2 degrees at a time rather than jumping several degrees at once, which can unnecessarily trigger backup heat modes.
If the system immediately reverts to emergency heat on its own after you switch it back to “Heat,” or it won’t respond at all, stop troubleshooting and call a licensed technician — especially if you smell burning, hear grinding, or the outdoor unit isn’t running at all.
When It’s Actually Fine (Don’t Panic)
Not every appearance of emergency heat means something is broken. It’s expected and harmless when:
● You manually turned it on because you already know the heat pump has a problem and you’re waiting for a technician — that’s exactly what the setting is for.
● A technician switched it on temporarily during a repair or while parts are on order.
● It ran briefly right after a power outage, while the system reset and re-established communication between the thermostat and outdoor unit.
● The distinction that matters: emergency heat should be a deliberate, temporary bridge — not a mystery setting that appeared on its own and won’t go away.
How Much Does Running Emergency Heat Actually Cost?
Emergency heat and auxiliary heat both rely on electric resistance heating, which is roughly 2 to 3 times less efficient than a heat pump’s normal compressor-driven operation. A few minutes here and there during a defrost cycle is negligible. But if emergency heat runs continuously for days — which happens when a homeowner manually activates it and forgets, or when a fault keeps forcing the system into it — that inefficiency compounds fast and can produce a very noticeable spike on your next electric bill. If your auxiliary or emergency heat seems to be running far more than a few minutes at a time, or your bill jumped without a matching cold snap, that’s a sign to have the system checked rather than waiting it out.
How to Prevent Unnecessary Emergency Heat Activation
1: Schedule annual maintenance. A yearly tune-up catches slow refrigerant leaks, weak capacitors, and dirty coils before they force a lockout.
2: Keep the outdoor unit clear. Maintain at least two feet of clearance from snow, mulch, and plant growth so airflow isn’t restricted.
3: Change air filters every 1–3 months. A clogged filter is one of the most common preventable causes of airflow-related faults.
4: Make gradual setpoint changes. Avoid jumping the thermostat several degrees at once; move it 1–2 degrees at a time to reduce unnecessary backup-heat triggers.
5: Upgrade to a smart or properly configured thermostat. Many can alert you the moment the system switches to backup heat, so you catch a developing fault early instead of discovering it on your electric bill.
Northern Virginia Factors That Make This More Likely
1: Age and sizing of the ductwork. Older Northern Virginia homes — many built before 1990 — often have ductwork that was never sized with a proper load calculation. Undersized or leaky ducts restrict airflow across the indoor coil, which can trigger pressure faults that shut the compressor down. If your home falls into that category, see our guide on why older Northern Virginia homes built before 1990 often have duct problems.
2: Heat pump sizing. A heat pump that’s undersized for the home will lean on backup heat constantly during cold snaps, wearing out the compressor faster and inflating bills. An oversized unit short-cycles, which stresses the compressor and can trip the same protective lockouts that force a switch to backup heat.
3: Winter temperature swings. Northern Virginia’s winters swing from mild 40s°F days to sudden hard freezes in the 10s and 20s°F. Heat pumps that are marginal on refrigerant charge or airflow tend to show problems first during these sharp cold snaps, which is exactly when emergency heat complaints spike.
4: Deferred maintenance. A heat pump that hasn’t had a tune-up in a year or more is more likely to have a slowly developing refrigerant leak, a dirty outdoor coil, or a weak capacitor — all of which show up as emergency heat lockouts once the coldest days of the season arrive.
What Golden Arrow Technicians Actually Check
When a Northern Virginia homeowner calls about a heat pump stuck on emergency heat, our technicians follow a consistent diagnostic path rather than guessing:
1: Confirm the thermostat mode and rule out an accidental manual switch first — it’s the fastest fix when it applies.
2: Check power at the outdoor disconnect and verify the breaker hasn’t tripped.
3: Inspect the outdoor unit for ice buildup and confirm whether the system is genuinely stuck in a failed defrost cycle.
4: Test refrigerant pressures and check for signs of a leak.
5: Test the compressor’s start components (capacitor, contactor) and confirm the compressor actually attempts to start.
6: Verify the reversing valve is shifting properly between heat and cool.
7: Check thermostat wiring, firmware, and settings if the unit was recently replaced or serviced by someone else.
How the Heat Pump Interacts With the Rest of Your System
Emergency heat problems rarely exist in isolation. If your heat pump has been running rough for a while, it’s worth checking related systems too. If the house has been unevenly heated even before emergency heat appeared, see our guide on heat pump not heating or cooling properly in Northern Virginia. If you’re weighing whether a heat pump is even the right long-term choice for your home, our guides on gas furnace vs. electric furnace for a Northern Virginia home and what type of heating system is best for a Northern Virginia home cover how heat pumps compare to the alternatives.
Red Flags When Vetting a Contractor for This Repair
● A company that quotes a repair price over the phone without ever inspecting the outdoor unit or checking refrigerant pressure.
● A technician who recommends full system replacement before diagnosing the actual cause of the emergency heat lockout.
● No written, itemized quote before work begins.
● No verification of licensing or insurance when asked directly.
● Pressure to sign a service agreement same-day, before any diagnostic has been performed.
How to Verify the Repair Actually Worked
After a technician clears the issue, confirm before they leave:
● The thermostat is switched back to normal “Heat” (not “Emergency Heat”), and the outdoor unit runs and produces warm air at the vents within a few minutes.
● Ask the technician to show you the refrigerant pressure readings and confirm they’re within manufacturer spec.
● Run the system through at least one full heating cycle while the technician is still on-site, if the weather allows it.
● Get the repair documented in writing, including what was replaced or adjusted, so there’s a record if the same issue recurs.
Get It Fixed Today
If your heat pump is stuck on emergency heat and you’re not sure why, don’t wait through another cold night guessing. Golden Arrow Service offers same-day diagnostic visits across Vienna, Fairfax, McLean, Arlington, and the rest of Northern Virginia, with a free second opinion if you’ve already had another company look at it and want to confirm the diagnosis before paying for a repair.
Golden Arrow Service
8740 Wolf Trap Road, Vienna, VA 22182
Call or text: (703) 782-5028
Find us on Google Maps: https://maps.app.goo.gl/SGtsKxsABCr4U7nm8
Frequently Asked Questions
Q1: Is it bad to run my heat pump on emergency heat all the time?
Yes. Emergency heat runs the electric backup strips (or furnace) as the sole heat source, which typically costs 2 to 3 times more per hour than normal heat pump operation. It’s meant to be a short-term bridge until the heat pump is repaired, not a permanent heating mode.
Q2: How do I turn off emergency heat on my thermostat?
Switch the thermostat’s system mode from “Emergency Heat” or “EM Heat” back to “Heat” or “Auto.” On a Google Nest thermostat, this is under Settings > Thermostat > Emergency Heat; on a Trane Home-connected system, it’s under System Mode > System Options > Emergency Heat > Off. The mode will not turn off on its own — you have to switch it manually once you know the heat pump is working again.
Q3: Why does my thermostat say “Emergency Heat” when it’s not even that cold outside?
This is one of the clearest signs of a problem. Auxiliary heat is designed to activate automatically in cold weather; true emergency heat should only be active because a person selected it. If your system shows emergency heat mode in mild 40s or 50s°F weather without anyone touching the thermostat, the heat pump likely has a fault — commonly a tripped breaker, refrigerant issue, or failed compressor.
Q4: How long does it take to diagnose a heat pump stuck on emergency heat?
A straightforward diagnostic — checking thermostat settings, breaker status, refrigerant pressure, and compressor operation — typically takes 30 to 60 minutes for a licensed technician. More complex issues, like a slow refrigerant leak or a failing reversing valve, may take longer to isolate.
Q5: Will a heat pump stuck on emergency heat damage the system?
Emergency heat mode itself won’t damage the heat pump, since the compressor is simply switched off. But whatever caused the system to need emergency heat in the first place — low refrigerant, a failing compressor, or ice buildup — can worsen if left unaddressed, so it’s worth having it diagnosed rather than leaving the system on backup heat indefinitely.
Q6: Does a dual-fuel (gas furnace + heat pump) system handle emergency heat differently?
Yes. In a dual-fuel setup, “emergency heat” typically forces the gas furnace to run as the sole heat source instead of electric strips, which is usually far less costly per hour than electric backup heat. The same rule still applies, though: if it’s running without you having switched it on, or won’t switch back, have the heat pump checked.
Q7: What’s the difference between emergency heat and a defrost cycle?
A defrost cycle is a normal, automatic process where the heat pump briefly reverses to melt ice off the outdoor coil, typically lasting 5 to 15 minutes, during which auxiliary heat may run to keep the house warm. Emergency heat is a separate, manually-activated mode that shuts the heat pump off entirely. If your system stays in what looks like a defrost cycle for much longer than 15 minutes, the defrost control or sensor may have failed.
Q8: How much more does emergency heat cost per month compared to normal operation?
It depends on how long it runs and your local electricity rate, but electric resistance backup heat is typically 2 to 3 times less efficient than a heat pump’s normal compressor-driven operation. Running it continuously for even a few days during a cold snap can add a noticeable spike to a monthly electric bill.