Heat Pump or Furnace Troubleshooting Guide (Troubleshooting Guide)

On this page

Quick answer
Confirm the symptom
Tools and prep
Step-by-step troubleshooting
Common causes table
Parts matching
When to call a pro
FAQ
Related guides

Quick answer

If your heat pump or furnace isn't heating, start by checking the thermostat settings and air filter. Ensure the power supply is stable and the emergency switch is on. If the system still doesn't work, inspect for error codes or unusual noises.

Confirm the symptom

No heat output from the system
System runs but doesn't warm the home
Unusual noises from the unit
Thermostat not responding
Error codes displayed on the system

Tools and prep

Screwdrivers (flathead and Phillips)
Thermal imaging camera or infrared thermometer
Replacement air filter
Flashlight
Multimeter for electrical checks
Service manual for the unit
Safety gloves and goggles

Step-by-step troubleshooting

Check Thermostat Settings
Do: Verify the thermostat is set to 'Heat' and the desired temperature is higher than the room temperature.
Observe: Thermostat displays correct settings and responds to input.
Means: Thermostat is functioning correctly.
Next: Move to step 2.
Inspect Air Filter
Do: Remove and examine the air filter for dirt or blockage.
Observe: Filter is clean or dirty.
Means: A dirty filter restricts airflow and reduces heating efficiency.
Next: Replace the filter if dirty and proceed to step 3.
Check Power Supply
Do: Ensure the unit's power switch is on and the circuit breaker hasn't tripped.
Observe: Power is stable and the unit responds to the thermostat.
Means: Power supply is not the issue.
Next: Proceed to step 4.
Look for Error Codes
Do: Check the unit's control panel for any displayed error codes.
Observe: Error codes or messages are visible.
Means: The system has a specific issue that needs attention.
Next: Refer to the service manual for code meanings and proceed to step 5.
Listen for Unusual Noises
Do: Turn on the system and listen for grinding, squealing, or rattling sounds.
Observe: Unusual noises are present or absent.
Means: Noises may indicate mechanical or electrical problems.
Next: If noises are present, contact a professional. If not, continue to step 6.
Inspect Emergency Switch
Do: Check the emergency shutoff switch near the unit to ensure it's in the 'On' position.
Observe: Switch is in the 'On' position.
Means: The emergency switch is not causing the issue.
Next: Move to step 7.
Check for Gas Supply (Furnace Only)
Do: Verify the gas supply valve is open and there are no gas leaks.
Observe: Gas valve is open and no gas smell is detected.
Means: Gas supply is available and safe.
Next: Proceed to step 8.
Test Blower Fan
Do: Turn on the system and check if the blower fan is running.
Observe: Blower fan is operational or not.
Means: A non-working blower fan prevents heat distribution.
Next: If the fan isn't working, contact a professional. If it is, continue to step 9.
Verify Heat Source Activation
Do: Check if the heat pump is switching to auxiliary heat or if the furnace burner is igniting.
Observe: Heat source is activating properly.
Means: The system is functioning as intended.
Next: If the heat source isn't activating, contact a professional.

Common causes

Cause	Likelihood	Difficulty	Part often needed
Dirty Air Filter A clogged filter restricts airflow, reducing heating efficiency.	Common	Easy	Air filter
Thermostat Malfunction A faulty thermostat may not send the correct signals to the heating system.	Sometimes	Medium	Thermostat
Tripped Circuit Breaker An electrical issue can cause the circuit breaker to trip, cutting power to the system.	Common	Easy	Circuit breaker
Gas Supply Issues (Furnace Only) A closed gas valve or leak can prevent the furnace from igniting.	Sometimes	Easy–Medium	Gas valve
Faulty Blower Fan A malfunctioning blower fan can't distribute heated air throughout the home.	Sometimes	Hard	Blower motor
Heat Pump Defrost Cycle Issues A heat pump stuck in defrost mode can't provide adequate heating.	Rare	Medium	Defrost control board
Ignition System Failure (Furnace Only) A faulty ignition system can prevent the furnace burner from lighting.	Sometimes	Hard	Ignition module
Refrigerant Leak (Heat Pump Only) Low refrigerant levels reduce the heat pump's ability to transfer heat.	Rare	Hard	Refrigerant
Thermostat Wiring Issues Loose or damaged wiring can disrupt communication between the thermostat and the system.	Sometimes	Medium	Thermostat wiring
System Age and Wear Older systems may have degraded components that affect performance.	Sometimes	Hard	System replacement

Parts matching

Common parts needed for heat pump or furnace issues include:

Air filter for improved airflow
Thermostat for accurate temperature control
Circuit breaker for power restoration
Gas valve for furnace gas supply
Blower motor for air distribution
Ignition module for furnace ignition
Defrost control board for heat pump operation

Always refer to your system's service manual for specific part compatibility and installation instructions.

When to call a professional

The system emits burning smells or gas odors
There are visible leaks or electrical sparks
Error codes persist after troubleshooting
The system makes loud or unusual noises
The unit fails to ignite or the blower fan doesn't work
You suspect a refrigerant leak in a heat pump
The system is over 15 years old and requires frequent repairs

FAQ

How often should I replace my air filter?

Replace the air filter every 1–3 months, depending on usage and filter type.

Can a thermostat cause my heat pump or furnace to stop working?

Yes, a malfunctioning thermostat can prevent the system from receiving signals to operate. Test or replace the thermostat if needed.

What should I do if my furnace won't ignite?

Check the gas supply, ensure the emergency switch is on, and look for error codes. If the issue persists, contact a professional.

Why is my heat pump not switching to auxiliary heat?

This could be due to a thermostat setting, low refrigerant levels, or a faulty defrost control board. Consult a professional for diagnosis.

How can I tell if my blower fan is working?

Listen for the fan's operation when the system is on. If it's silent or making odd noises, the motor may need repair or replacement.

Is it normal for my heat pump to make noise during the defrost cycle?

Yes, some noise is normal during defrost cycles, but loud or continuous noises may indicate a problem.