Why Is My Heat Pump Showing an LP (Low Pressure) Code? – Intermatic Support

Applies To

All AHN and Traditional Series Heat Pumps

Why is my heat pump showing an LP (Low Pressure) code?

The LP code indicates low pressure in the refrigeration system and may be related to one or more of these issues:

Cold ambient temperatures that are below the normal operating range of the heat pump, typically below 50° F (10° C).
A refrigerant leak or low refrigerant charge.
An issue with the low-pressure switch or its wiring.
An issue with the fan motor or fan capacitor.
A problem with the TXV (thermal expansion valve).
A clogged or dirty evaporator coil that restricts airflow.
In some cases, a control board issue.

Confirm Outdoor Temperature
If the heat pump is showing an LP code and the ambient temperature is below 50° F (10° C), it is likely too cold for the heat pump to operate. Allow the temperature to rise above 60° F (16° C), then restart the heat pump and observe whether the LP code clears.
Inspect and Clean the Evaporator Coil
Check the outside evaporator coil for dirt, leaves, or other debris. Using a garden hose, gently spray the outside of the coil to remove any debris and restore proper airflow. Do not use high pressure, as this can damage the fins.
Restart the Heat Pump and Observe Operation
After confirming that outdoor temperatures are within the normal operating range and the evaporator coil is clean and unobstructed, restart the heat pump and verify whether the LP code returns.
Contact Intermatic Technical Support if the LP Code Remains
If the LP code remains after these checks, contact Intermatic Technical Support for further assistance. Additional diagnostics may be required by a qualified technician to check refrigerant charge, pressure switches, wiring, or internal components.

If the LP code appears during colder temperatures, allow the outdoor temperature to rise into the normal operating range before restarting the heat pump.
Always keep the evaporator coil and surrounding area free of debris to help maintain proper airflow and reduce the likelihood of LP codes.
If the issue is not related to ambient temperature or airflow, the LP code could be caused by a refrigerant leak, an issue with the low-pressure switch or its wiring, a fan motor or capacitor issue, a problem with the TXV, or a control board issue. These conditions should be evaluated by a qualified technician.
For ongoing issues or if you are unsure how to proceed, contact Intermatic Technical Support for guidance.