Heat Pump Not Coming On in Heat Mode (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

First, check the thermostat settings. Ensure it's set to 'Heat' mode and the temperature is higher than the current room temperature. If that's correct, verify the power supply and circuit breakers. If these steps don't resolve the issue, follow the troubleshooting steps below.

Confirm the symptom

Thermostat set to 'Heat' but no warm air is coming out.
Heat pump doesn't turn on when 'Heat' mode is selected.
No error codes displayed on the thermostat or heat pump.
Other heating modes (like 'Cool') work fine.
Outdoor unit is not running.

Tools and prep

Screwdriver (flathead and Phillips)
Multimeter
Ladder (if needed to access outdoor unit)
Owner's manual for your heat pump
Turn off power to the heat pump at the circuit breaker.
Ensure the area around the outdoor unit is clear of debris.

Step-by-step troubleshooting

Check Thermostat Settings
Do: Ensure the thermostat is set to 'Heat' mode and the temperature is set higher than the current room temperature.
Observe: If the settings are correct, proceed to the next step.
Means: Incorrect settings are the issue.
Next: Check Power Supply
Check Power Supply
Do: Verify that the power is on at the circuit breaker and that the breaker hasn't tripped.
Observe: If the breaker is tripped, reset it and see if the heat pump turns on.
Means: Power issue resolved.
Next: Check for Error Codes
Check for Error Codes
Do: Look at the thermostat and outdoor unit for any error codes.
Observe: If there are error codes, consult the owner's manual for specific troubleshooting steps.
Means: Error code indicates a specific issue.
Next: Inspect Outdoor Unit
Inspect Outdoor Unit
Do: Ensure the outdoor unit is clear of debris and has proper airflow.
Observe: If the unit is clear, proceed to the next step.
Means: Blocked airflow was the issue.
Next: Check Reversing Valve
Check Reversing Valve
Do: Listen for the reversing valve to engage when switching from 'Cool' to 'Heat' mode.
Observe: If you don't hear the valve engage, it may be faulty.
Means: Reversing valve needs replacement.
Next: Check for Frozen Coils
Check for Frozen Coils
Do: Inspect the outdoor unit for frozen coils.
Observe: If coils are frozen, defrost them according to the manufacturer's instructions.
Means: Frozen coils were the issue.
Next: Check Defrost Control Board
Check Defrost Control Board
Do: Use a multimeter to test the defrost control board for continuity.
Observe: If there is no continuity, the board may need replacement.
Means: Defrost control board is faulty.
Next: Check for Low Refrigerant
Check for Low Refrigerant
Do: Look for signs of low refrigerant, such as ice buildup or hissing noises.
Observe: If low refrigerant is suspected, contact a professional.
Means: Low refrigerant is the issue.
Next: Call a Professional

Common causes

Cause	Likelihood	Difficulty	Part often needed
Incorrect Thermostat Settings The thermostat may be set to 'Cool' mode or the temperature setpoint is too low.	Common	Easy	None
Tripped Circuit Breaker The circuit breaker may have tripped, cutting power to the heat pump.	Common	Easy	None
Faulty Reversing Valve The reversing valve may not be engaging properly when switching to 'Heat' mode.	Sometimes	Medium	Reversing Valve
Frozen Coils The outdoor coils may be frozen, preventing the heat pump from operating in 'Heat' mode.	Sometimes	Easy–Medium	None
Faulty Defrost Control Board The defrost control board may not be functioning properly, causing the heat pump to malfunction in 'Heat' mode.	Rare	Hard	Defrost Control Board
Low Refrigerant Low refrigerant levels can prevent the heat pump from operating in 'Heat' mode.	Rare	Hard	Refrigerant

Parts matching

If you've identified a faulty part, here are some details to help you find the right replacement.

Reversing Valve: Ensures the heat pump can switch between heating and cooling modes.
Defrost Control Board: Manages the defrost cycle to prevent frozen coils.
Refrigerant: Essential for the heat transfer process in the heat pump.
Thermostat: Controls the temperature settings and mode of the heat pump.
Circuit Breaker: Protects the electrical system from overloads and short circuits.
Multimeter: Useful for testing electrical components like the defrost control board.

Always ensure you purchase parts that are compatible with your specific heat pump model.

When to call a professional

If you suspect low refrigerant levels.
If the defrost control board is faulty.
If the reversing valve needs replacement.
If you're not comfortable performing the troubleshooting steps yourself.
If the heat pump still doesn't work after following all the steps.
If there are any unusual noises or smells coming from the heat pump.

FAQ

Why won't my heat pump turn on in heat mode?

Common reasons include incorrect thermostat settings, tripped circuit breakers, faulty reversing valves, frozen coils, faulty defrost control boards, or low refrigerant levels.

How do I reset my heat pump?

Turn off the power at the circuit breaker, wait for a few minutes, and then turn it back on. Check if the heat pump turns on in 'Heat' mode.

Can I fix a faulty reversing valve myself?

Replacing a reversing valve can be complex and may require professional assistance. If you're not experienced, it's best to call a professional.

What should I do if my heat pump's coils are frozen?

Follow the manufacturer's instructions to defrost the coils. This usually involves turning off the heat pump and allowing the ice to melt naturally.

How do I know if my heat pump has low refrigerant?

Signs of low refrigerant include ice buildup on the coils, hissing noises, and reduced heating or cooling performance. If you suspect low refrigerant, contact a professional.

Why is my heat pump making unusual noises?

Unusual noises can indicate a variety of issues, such as a faulty compressor, loose parts, or debris in the system. Turn off the power and contact a professional for inspection.