When the heat pump’s emergency heat system fails, it can jeopardize home comfort during extreme cold. Emergency heat serves as a backup for the main heating system, and resolving its failure quickly is crucial. This guide explains the most common causes, troubleshooting strategies, and repair options for homeowners facing this issue, with a special focus on American settings and equipment.
Summary Table: Emergency Heat Failure Quick Reference
| Potential Cause | Symptoms | Suggested Action | DIY Safe? |
|---|---|---|---|
| Broken Thermostat | No response when switched to emergency heat | Check/replace batteries; recalibrate or replace thermostat | Yes |
| Tripped Circuit Breaker | No power to heat strips or air handler | Reset breaker and watch for repeat trips | Yes |
| Faulty Heat Strips | Blower runs cold; emergency heat won’t engage | Test and replace heat strips as needed | No (call HVAC pro) |
| Defective Contactor/Relay | System tries to switch modes but fails; possible buzzing noise | Visual inspection and electrical testing | No (call HVAC pro) |
| Loose/Damaged Wiring | Intermittent or no emergency heat operation | Check connections (power off!) | Limited (pro advised) |
| Control Board Failure | System unresponsive in EM mode, other electrical issues | Diagnostic test, replace if needed | No (call HVAC pro) |
How Emergency Heat Works In Heat Pumps
A heat pump extracts heat from outside air to warm the home efficiently. When temperatures drop drastically, its efficiency diminishes. The emergency heat (or EM heat) setting activates an electric resistance backup system or, for some models, a gas furnace). This backup provides direct heat rapidly, ensuring the home remains warm during critically cold weather or while the main heat pump is malfunctioning. It is intended for short-term, emergency use rather than daily operation due to significantly higher energy costs.
Understanding Emergency Heat Vs. Auxiliary Heat
It’s key to distinguish between “auxiliary heat” and “emergency heat.” Both provide supplemental warmth, but with a difference: Auxiliary heat (AUX heat) turns on automatically when the heat pump can’t meet the thermostat’s setpoint, while emergency heat requires a manual setting by the homeowner. Emergency mode bypasses the heat pump entirely, relying solely on backup heat, often electric strips.
Main Reasons Emergency Heat Is Not Working
Thermostat Issues
The thermostat acts as the control center. If it malfunctions, the emergency heat system may fail. Battery depletion, calibration errors, software malfunctions, or physical damage are common reasons. Sometimes, an incompatible or misconfigured thermostat is at fault, especially if recently replaced.
Circuit Breaker Or Fuse Problems
The emergency heat circuit draws far more power than normal heat pump operation. Tripped breakers, blown fuses, or overloaded circuits can instantly disable emergency heat capabilities. These issues are particularly common in older homes with aging electrical panels.
Failed Heating Elements (Heat Strips)
Electric heating elements, or “heat strips,” convert electricity directly into heat. Years of operation or electrical surges can cause them to burn out, short-circuit, or become disconnected. Unlike heat pumps, there is no mechanical component to repair—the entire strip must be replaced if faulty.
Defective Relays Or Contactors
Relays and contactors are electronic switches that direct power to heating elements or the blower motor. If a relay sticks, burns, or fails, the backup heating system may not receive the necessary voltage. Audible clicking, humming, or buzzing without operation is often a warning sign.
Damaged Or Loose Wiring
Over time, electrical wires supplying power to the air handler, heat strips, or thermostat can loosen, corrode, or break. This interrupts the circuit. Accidental damage during attic or crawlspace work also accounts for such failures.
Faulty Control Board
Most modern HVAC equipment uses a computer-style circuit board to manage complex heating cycles. A control board failure can prevent the system from recognizing the emergency heat command, leaving the home cold despite the thermostat setting.
Step-By-Step Troubleshooting Guide
Before calling an HVAC technician, there are several safe troubleshooting steps a homeowner can perform. Always turn off power at the breaker panel before opening any equipment panels.
Check The Thermostat
- Switch the thermostat to “EM” or “Emergency Heat” mode. Ensure the setting registers on the display.
- Replace batteries with fresh, high-quality ones.
- Double-check that your thermostat is compatible with heat pump systems and was properly installed.
- If programmable, review schedule settings that may override manual commands.
A non-responsive display or failure to click when adjusted may point to thermostat replacement.
Inspect Circuit Breakers And Fuses
- Locate your main breaker panel. Identify breakers marked for “Air Handler,” “Heat Strips,” or “Furnace.”
- Flip each associated breaker firmly off, wait a few seconds, then switch back on.
- Check for repeat trips, which suggest a deeper electrical fault or short.
- Some systems also have fuses located at the air handler or control board; replace any that appear darkened or broken.
If breakers continue to trip after reset, stop and consult a licensed electrician or HVAC professional.
Test Emergency Heat Activation
- Set thermostat high (5+ degrees above current temperature) in “EM” heat mode.
- Listen for the air handler and blower to start. Within a few minutes, the vents should blow warm air.
- If the fan runs but air remains cold, there may be a problem with the heat strips or relay—professional help is usually required.
Inspect For Visual Wiring Or Component Issues
- Open the air handler (with power off!). Look for signs of burnt wires, disconnected terminals, or loose connections.
- Locate the heat strips—these usually look like coiled wires attached to ceramic supports. Melted, broken, or burned elements are signs of failure.
- Check the relay and control board for scorch marks, corrosion, or cracked solder joints.
Do not attempt repair if unfamiliar with high-voltage components—these can be dangerous.
When To Call A Licensed HVAC Technician
Emergency heat failures can involve high-voltage elements and sophisticated electronics. If you cannot resolve the problem by checking the thermostat and breakers, professional diagnosis is strongly advised. Certified technicians can measure voltage, amperage, resistance, and use computer diagnostics to pinpoint faults. In some states, attempting to repair electrical HVAC components without a license may be prohibited.
Common HVAC Technician Diagnostic Steps
- Inspect and Test Heat Strips: Use a multimeter to measure resistance and ensure continuity.
- Check Relays and Contactors: Activate manually to confirm switching function and voltage delivery.
- Test Control Board: Analyze diagnostic LEDs or error codes; check outputs for correct voltage on EM heat demand.
- Wiring Assessment: Trace all high-voltage and control wires for integrity and tightness.
- Evaluate System Compatibility: Confirm that thermostats, boards, and backup heat are correctly matched for the heat pump model.
Comprehensive diagnostic reports are usually provided for homeowner records.
Repair And Replacement Options
Depending on the findings, several repair strategies may apply:
- Thermostat Replacement: Modern programmable thermostats compatible with your system enhance energy efficiency and reliability.
- Heat Strip Replacement: Faulty electric elements are typically swapped out as a set; costs depend on system wattage and accessibility.
- Electrical Repairs: Re-securing wire connections, replacing corroded or melted wires, and updating breakers or fuses solves many power supply problems.
- Control Board Replacement: If the board fails diagnostics, a like-for-like model ensures system compatibility and restores all functions.
Always use OEM parts or certified aftermarket components for repairs; improper parts could void warranties or reduce system life.
How To Prevent Future Emergency Heat Failures
Annual HVAC Maintenance
Proactive maintenance—conducted every fall—reduces the risk of surprise breakdowns. Technicians clean electrical contacts, test relays, tighten wires, and verify that backup heat strips receive sufficient current. A maintenance plan also includes checking ductwork for leaks and replacing air filters, which contribute to overall heat pump efficiency.
Thermostat Upgrades And Battery Changes
Replace thermostat batteries yearly, or whenever the display dims. Smart thermostats offer self-diagnosis features, alerts, and even remote monitoring via smartphone, streamlining troubleshooting before emergencies arise.
Monitor Circuit Breakers And Home Electrical Load
Heavy electrical usage—like space heaters, microwaves, or EV chargers—can put strain on older electrical systems. If circuit breakers supplying the air handler or heat strips trip, avoid plugging high-wattage devices into the same circuit. An electrician can map your circuits and recommend upgrades if needed.
Protect Against Power Surges
Lightning strikes and grid surges may damage sensitive control boards or burn out heat strips. Whole-home surge protectors and routine electrical inspections significantly reduce risks, particularly in areas prone to electrical storms.
Frequently Asked Questions About Heat Pump Emergency Heat
Is Emergency Heat More Expensive Than Normal Heat Pump Operation?
Yes—emergency heat typically uses electric resistance strips, which are far less efficient than the heat pump’s normal refrigerant-based cycle. It should be used only as a last resort, as bills can rise sharply in just a few days of use.
How Will I Know If The Emergency Heat Is Actually Running?
- The thermostat should visibly show “EM heat” or a red light.
- Air from vents will quickly become noticeably warmer, often within 2-3 minutes.
- The outdoor heat pump unit should remain silent (not running), since only the backup system is in use.
Unexpectedly cold or neutral air suggests a malfunction requiring attention.
Can I Leave Emergency Heat On All Winter?
No—this mode is only for short-term/emergency situations. Extended use leads to high energy consumption and increased wear on electrical heating elements. Restore the heat pump to standard operation as soon as possible.
What Should I Do If I Smell Burning When Emergency Heat Turns On?
Some odor is normal if the system hasn’t run for several months due to collected dust burning off. However, persistently strong, acrid, or smoky odors require immediate shutdown and professional inspection to prevent fire risk.
What Is The Difference Between “Emergency Heat” And “Backup Heat”?
They are often used interchangeably, but technically: “Emergency Heat” is manual, user-activated, and bypasses the heat pump entirely; “Backup Heat” may refer to either the auxiliary or emergency system, depending on context and system design.
Professional Tips For Homeowners
- Document all maintenance, repairs, and upgrades—this speeds professional diagnostics during emergency calls.
- Keep your HVAC system’s make, model, and serial number handy for service inquiries.
- In severe weather, avoid crowding vents or blocking airflow to registers and returns.
- If planning to replace an older system, ask your installer about improved backup heat options—many new models boost efficiency and reliability.
Regional Considerations: Heat Pump Emergency Heat In The U.S.
Some American climates, especially across the South and West, rarely need emergency heat due to milder winters. However, in New England, Midwest, and Mountain states, efficient emergency heat operation is essential for safety, especially in rural or remote areas prone to power outages. Homeowners in colder zones should schedule professional maintenance every fall and familiarize themselves with backup heating features.
Key Takeaways
- Emergency heat is a critical backup for heat pump systems and demands immediate attention if it fails.
- Common causes include thermostat issues, electrical faults, failed heat strips, or defective control boards.
- Quick troubleshooting can resolve battery, breaker, or basic thermostat errors, but larger repairs should be done by a licensed HVAC professional.
- Annual maintenance and smart upgrades can prevent most emergency heating failures and improve peace of mind throughout winter.