Lennox Furnace Error Code E370

E370 means the furnace detected that its interlock switch was in the open position for two continuous minutes. The interlock switch monitors whether access panels and doors are properly closed. The furnace shuts down when this safety circuit is open to prevent unsafe operation. The alarm clears when 24VAC is continuously sensed on the DS terminal for at least 10 seconds, or after a power reset.

Yes, the interlock switch circuit is a safety feature designed to prevent the furnace from operating with access panels open or unsecured. The E370 alarm indicates this safety loop is broken, which is why the furnace shuts down automatically. Do not attempt to bypass or defeat the interlock switch, as it protects against exposure to high-voltage components, combustion gases, and moving parts.

If the fix is simply reseating a loose access panel, there is no parts cost and minimal labor involved. If the interlock switch itself needs replacement, parts typically range from around $15 to $60 depending on the specific switch, plus any labor charges. A control board replacement, if required in more serious cases, can range from $200 to $600 or more for parts alone. Having a qualified HVAC technician diagnose the specific cause first will help avoid unnecessary parts costs.

Start by terminating any active service operations and checking that all furnace access panels and doors are fully closed and properly latched. If the panels are secure and the error persists, a technician should test the interlock switch for proper mechanical actuation and verify that 24VAC is present on the DS terminal on the control board. Faulty switches or wiring in the interlock circuit will need to be repaired or replaced.

A power reset can clear the E370 alarm, but the alarm will return if the underlying cause is not corrected. The alarm also clears automatically if 24VAC is continuously present on the DS terminal for a minimum of 10 seconds after the interlock switch closes. Simply resetting without addressing the root cause will result in the error returning once the furnace attempts to operate again.