On this page
Quick answer
If your heat pump won't start, first check the power supply and thermostat settings. Reset the circuit breaker if tripped, and ensure the emergency switch is on. If these don't work, inspect the capacitor or contact a professional.
Confirm the symptom
- Heat pump does not turn on at all
- No fan or compressor noise when activated
- Thermostat shows no response from the unit
- Power is confirmed to be on but unit remains off
Tools and prep
- Voltage tester
- Screwdriver set
- Flashlight
- Safety gloves and goggles
- Owner's manual for the heat pump
- Thermometer (optional for temperature checks)
Step-by-step troubleshooting
- Check Power SupplyDo: Verify the circuit breaker for the heat pump is on and not tripped.Observe: Breaker is in the 'on' position.Means: Power supply is intact.Next: If the breaker is off, reset it and try starting the heat pump again.
- Inspect Emergency SwitchDo: Locate and check the emergency shutoff switch near the outdoor unit.Observe: Switch is in the 'on' position.Means: The unit is not manually turned off.Next: If the switch is off, turn it on and attempt to restart the heat pump.
- Test Thermostat SettingsDo: Ensure the thermostat is set to 'heat' mode and the temperature is set higher than the room temperature.Observe: Thermostat is correctly configured to trigger heating.Means: Thermostat is functioning as intended.Next: If settings are correct but the unit still doesn't start, proceed to the next step.
- Check for Error CodesDo: Look at the thermostat or heat pump control panel for any displayed error codes.Observe: Error code is visible.Means: The unit may have a specific issue that needs addressing.Next: Refer to the owner's manual to interpret the error code and take appropriate action.
- Inspect CapacitorDo: Turn off power to the unit and use a voltage tester to check the capacitor for proper function.Observe: Capacitor shows no visible signs of damage and holds charge.Means: Capacitor is likely functioning.Next: If the capacitor is damaged, it may need replacement by a professional.
- Examine ContactorDo: Open the electrical panel and visually inspect the contactor for signs of wear or damage.Observe: Contactor is clean and shows no signs of burning or corrosion.Means: Contactor is in good condition.Next: If the contactor is damaged, it may need replacement by a qualified technician.
- Check AirflowDo: Ensure there is no obstruction around the outdoor unit and that the air filter is clean.Observe: Airflow is unrestricted and filter is clean.Means: Airflow is not the issue.Next: If airflow is restricted, clear any obstructions and clean the filter.
Common causes
| Cause | Likelihood | Difficulty | Part often needed |
|---|---|---|---|
| Tripped Circuit Breaker The heat pump may have drawn too much power, causing the breaker to trip. | Common | Easy | None |
| Emergency Shutoff Switch Off The manual switch near the outdoor unit could have been accidentally turned off. | Common | Easy | None |
| Thermostat Malfunction A faulty thermostat may not send the correct signal to the heat pump. | Sometimes | Easy–Medium | Thermostat |
| Failed Capacitor A bad capacitor can prevent the motor from starting. | Sometimes | Medium | Capacitor |
| Faulty Contactor A damaged contactor can interrupt the electrical flow to the motor. | Sometimes | Medium | Contactor |
| Low Refrigerant Low refrigerant levels can cause the system to shut down to prevent damage. | Rare | Hard | Refrigerant (requires professional handling) |
| Frozen Coils Frozen coils can prevent the heat pump from operating properly. | Rare | Medium | Defrosting tools or professional service |
Parts matching
If your troubleshooting confirms a part failure, here are common replacements:
- Thermostat: Replace if it's not sending signals correctly.
- Capacitor: Install a new one if the existing one is swollen or leaking.
- Contactor: Replace if it shows signs of burning or sticking.
- Air Filter: Clean or replace if it's clogged and restricting airflow.
- Emergency Switch: Install a new switch if it's faulty or damaged.
Always match the part specifications to your heat pump model and consult the owner's manual for installation instructions.
When to call a professional
- If the heat pump still doesn't start after checking all power sources and basic components
- If you detect refrigerant leaks or smell a chemical odor
- If the unit makes loud or unusual noises when attempting to start
- If error codes persist or indicate complex issues
- If you're uncomfortable working with electrical components or high-voltage systems
FAQ
Can a tripped circuit breaker cause my heat pump not to start?
Yes, a tripped breaker cuts power to the unit. Resetting it may restore function.
What should I do if my thermostat is set correctly but the heat pump doesn't respond?
Check the thermostat's batteries and wiring. If it's faulty, replace it with a compatible model.
Is it safe to replace a capacitor myself?
Capacitors store electrical charge. If you're experienced, you can replace it, but it's safer to call a professional.
Why is my heat pump making a humming noise but not starting?
A humming sound often indicates a failed start capacitor or a seized motor.
How do I know if my heat pump has low refrigerant?
Low refrigerant usually causes reduced heating performance and may trigger error codes. A professional must recharge it.