Heat Pump Emergency Heat Not Working: Causes and Fixes

The emergency heat function on a heat pump activates backup heating when the system cannot deliver enough warmth. When emergency heat does not work, indoor comfort and safety can be at risk. This article explains common causes, step-by-step troubleshooting, temporary workarounds, repair options, and preventive maintenance to restore reliable heating.

Symptom	Likely Cause	Quick Action
No heat when emergency heat is selected	Thermostat settings, blown breaker, or failed backup heat strips	Check thermostat mode, inspect breaker, reset if safe
Outdoor unit frozen or noisy	Compressor or defrost issues	Turn off outdoor unit, call technician
Higher-than-expected electric bills	Auxiliary strips running continuously	Verify thermostat setpoint and wiring

How Emergency Heat Works On A Heat Pump

Emergency heat is a manual thermostat mode that bypasses the heat pump and runs the backup heating source, typically electric resistance strips or a gas/oil furnace. It is intended for use when the heat pump cannot operate, such as during a major malfunction or when outdoor temperatures make the heat pump ineffective.

Key point: Emergency heat consumes more energy than the heat pump, so it is for temporary use or true system failure.

Common Reasons Emergency Heat Is Not Working

Thermostat Mode Or Configuration Errors

The thermostat must be explicitly set to EMER (Emergency Heat) for the backup heat to engage. Some thermostats and smart controls label modes differently or require a separate Aux/Emer setting. Incorrect mode, scheduling conflicts, or battery issues can prevent activation.

Blown Circuit Breaker Or Tripped Disconnect

Backup electric strips and indoor furnace components typically have dedicated breakers or fuses. A tripped breaker at the main panel or a blown fuse at the furnace will render emergency heat inoperative until power is restored.

Failed Electric Heat Strips Or Furnace Ignition Problems

Electric resistance strips can fail due to age or overheating. Gas or oil furnaces used as backups may have pilot, ignition, or gas valve issues. A malfunctioning component will prevent emergency heat from producing warm air.

Thermostat Wiring Or Control Board Failures

Faulty wiring between the thermostat and the indoor unit or damaged relay/contactor on the furnace control board can stop the backup heat from receiving the signal to turn on. Corroded terminals and loose wires are common culprits.

Reversing Valve Or Compressor Problems Confusing The System

If the heat pump is stuck in cooling mode or the reversing valve is malfunctioning, the system may not switch to emergency heating correctly. Although emergency heat bypasses the outdoor unit, control interlocks or errors can block the function.

Low Refrigerant, Frozen Outdoor Coil, Or Defrost Malfunctions

Severe outdoor coil freezing or refrigerant issues can cause protective controls to lock out heating. Some systems use safety interlocks that prevent the backup heat from engaging until the outdoor fault is cleared.

Age And Component Wear

Older systems are more likely to suffer multiple simultaneous failures: failing thermostats, worn heating elements, degraded relays, and clogged air filters that limit airflow and trigger safeties preventing emergency operation.

Symptoms And Diagnosis Checklist

• No response when thermostat set to EMER: check thermostat, breakers, and wiring.
• Indoor fan runs but air is cold: backup heating elements not energizing or furnace not igniting.
• Thermostat shows call for heat but no heat delivered: possible relay/fuse or control board failure.
• Outdoor unit frozen or noisy: may indicate primary heat pump failure; emergency heat should still operate but may be interlocked.

Step-By-Step Troubleshooting For Homeowners

1. Verify Thermostat Settings

Confirm the thermostat is set to EMER (Emergency Heat) and not AUX or HEAT. Consult the thermostat manual for correct operation; some models require pressing a mode button or changing a configuration setting to enable emergency heat.

2. Inspect Power And Breakers

Check the main electrical panel for tripped breakers related to the furnace, electric heat strips, and outdoor unit. Reset tripped breakers only once; if a breaker trips again immediately, leave it off and call a technician.

3. Check Furnace Switches And Fuses

Locate the furnace or air handler switch and the auxiliary heat fuses or high-limit safeties. Replace blown fuses with the exact rating and do not bypass safety devices.

4. Observe Indoor Air Handler Operation

With emergency heat selected, confirm the air handler fan is running and check if heat strips glow (if visible) or if combustion occurs in a gas furnace. No heat from the registers with the fan running points to failed heat sources or control issues.

5. Listen For Relays And Contactors

When the thermostat calls for emergency heat, listen near the furnace for clicking relays or the contactor engaging. No click suggests wiring, thermostat signal, or control board problems.

6. Inspect Thermostat Wiring

Turn off power and remove the thermostat cover to check for loose or corroded wires on the emergency heat terminal (often labeled E or AUX). Reattach secure connections and restore power.

When To Use Temporary Workarounds

If emergency heat fails during extreme cold, temporary measures can maintain safety while arranging professional repairs. Use space heaters in occupied rooms, seal drafts, layer clothing, and prioritize sleeping areas for heating. Avoid using ovens or risky heating methods.

Safety note: Use portable electric heaters with built-in safety features and never leave them unattended.

Repair Options And Typical Costs

Costs vary depending on the root cause. Replacing thermostat components or repairing wiring is relatively affordable. Replacing electric heat strips, contactors, or control boards increases cost. Full furnace or compressor replacement is most expensive.

Repair	Typical Cost Range (US)
Thermostat diagnosis/replace	$100–$400
Thermostat wiring/relay repair	$150–$500
Replace electric heat strips	$300–$1,000
Gas furnace ignition/repair	$200–$1,200
Control board replacement	$300–$1,000
Major system replacement	$3,500–$12,000+

When To Call An HVAC Technician

Call a licensed HVAC technician if homeowners identify blown fuses, repeated breaker trips, failed ignition on a gas furnace, electrical faults, refrigerant leaks, or compressor issues. Professional diagnosis prevents unsafe DIY attempts and ensures proper repairs.

Recommended: Call a licensed, insured technician for electrical, gas, or refrigerant work, and request a written estimate before authorizing repairs.

Preventive Maintenance To Keep Emergency Heat Reliable

Regular maintenance reduces the likelihood of emergency heat failing during cold weather. Scheduled servicing should include thermostat calibration, inspection of auxiliary heating elements, tightening of electrical connections, testing of safeties, and cleaning air filters and coils.

• Replace air filters every 1–3 months.
• Have the system serviced annually in fall before the heating season.
• Inspect thermostat batteries and settings seasonally.
• Clear debris around outdoor units to prevent freezing and airflow issues.

Smart Thermostats, Settings, And Common Pitfalls

Smart thermostats can complicate emergency heat use. Some will automatically call for backup heat when outdoor temperatures drop, while others reserve EMER for manual selection. Incorrect wiring, firmware glitches, or energy-saving algorithms can prevent emergency heat from operating.

Tip: Ensure the smart thermostat is set up for heat pump systems and that the installer correctly configured the AUX/E and compressor control settings.

Energy Considerations And Best Practices

Emergency heat is significantly less efficient than a heat pump. Prolonged use increases electric bills and can overload the electrical system. Use emergency heat only when necessary and prioritize repairing the heat pump to restore efficient heating.

Best practice: After repairs, verify the system cycles between heat pump and auxiliary heat correctly, and monitor energy use to confirm efficiency.

Common Misdiagnoses And How To Avoid Them

Homeowners often mistake auxiliary heat operation for heat pump failure. If auxiliary heat runs while the heat pump can still operate, the thermostat may be using AUX as part of normal operation. Understanding the difference between AUX (automatic supplemental heat) and EMER (manual emergency heat) prevents unnecessary repairs.

Avoid: Changing system components without confirming the root cause; always run systematic diagnostics or consult a professional.

Checklist For When The Technician Arrives

1. Document symptoms, previous troubleshooting steps, and thermostat behavior.
2. Note when issues began and any unusual noises or odors.
3. Provide access to the furnace, outdoor unit, and main electrical panel.
4. Ask for an explanation of findings, repair options, expected lifespan, and energy implications.

Frequently Asked Questions

Why Does Emergency Heat Use So Much Electricity?

Emergency heat typically uses electric resistance elements that convert electricity directly into heat, which is less efficient than transferring heat via a compressor-driven heat pump. This results in higher consumption and costs.

Can A Heat Pump Run Emergency Heat And The Heat Pump Together?

Most systems will not run emergency heat simultaneously with the heat pump. EMER is designed to bypass the heat pump, but auxiliary heat (AUX) may run alongside the heat pump during very cold conditions to support heating capacity.

Is It Safe To Manually Toggle Emergency Heat If The Heat Pump Fails?

Yes, it is safe to select EMER if the system is designed for it and the backup heating source is functioning. First check breakers and visible components. If unsure, consult a technician to avoid electrical or combustion hazards.

Key Takeaways For Homeowners

Emergency heat failure can stem from simple issues (thermostat mode, tripped breaker) or complex faults (failed heat strips, control board or furnace ignition). Systematic troubleshooting narrows the cause quickly.

Prioritize safety: Avoid disabling safeties, never bypass electrical devices, and rely on licensed technicians for gas, electrical, or refrigerant repairs.

Proper maintenance, correct thermostat setup, and early diagnosis keep emergency heat reliable and protect comfort during cold weather without unnecessary energy cost.