Lennox Heat Pump Error Code 4

Error code 4 means the low or high pressure switch opened within the first two minutes of compressor operation. The control board shuts the compressor down to prevent damage when pressure readings fall outside the safe operating range that quickly. Common causes include low refrigerant charge, fan failure, or blocked airflow through the coils. A technician should inspect the unit and check system pressures before restarting.

No, you should not continue operating the heat pump once this fault is active. The pressure switches are designed to protect the compressor from running under conditions that can cause irreversible mechanical damage. Repeatedly attempting to restart the unit without resolving the underlying cause risks compressor failure, which is one of the most expensive repairs on a heat pump system.

Repair costs vary widely depending on the root cause. Cleaning a blocked coil or replacing a dirty filter is inexpensive, typically in the range of $50 to $150 for a service call. A refrigerant recharge can cost anywhere from $150 to $500 or more depending on the refrigerant type and quantity needed. Fan motor replacement typically ranges from $200 to $600 in parts and labor, while a failed compressor can cost $1,000 to $2,500 or higher.

Some causes, like a dirty air filter or debris blocking the outdoor unit, can be addressed without professional help. However, diagnosing refrigerant charge issues, repairing fan motors, or replacing pressure switches requires specialized tools and, in the case of refrigerant work, an EPA Section 608 certification. If a basic airflow check does not resolve the fault, contact a licensed HVAC technician.

A reset may temporarily clear the fault and allow the unit to attempt startup again, but the code will return if the underlying cause has not been corrected. If the pressure switch opens again within two minutes of compressor startup, the system will shut down and log the fault again. A reset is useful for confirming the fault is repeatable, but it is not a fix.