Furnace shuts down with E4, high temperature warning, burner stops and blower may continue running

Safety first: Turn off power before removing blower doors or panels. Surfaces may be hot.

Steps:

• Check air filter: Locate the furnace air filter in the return air duct or blower compartment. Remove and inspect. Replace if dirty or clogged. A restricted filter is a common cause of high limit trips.
• Inspect supply and return vents: Ensure all supply registers and return grilles are open and not blocked by furniture, rugs, or covers.
• Verify blower operation: With panels in place and power restored, set the thermostat to call for heat and observe if the main circulation blower starts after the burner ignites. If the blower does not run, the blower motor, capacitor, or Danfoss fan control relay may be faulty.
• Check high limit switch: With power off, locate the high limit thermostat on the heat exchanger panel. Inspect wiring for loose connections. Some manual-reset limits have a small red button; if present and tripped, press to reset once. Repeated trips indicate an underlying airflow or heat exchanger issue.
• Reset controller: After correcting airflow issues, reset the Danfoss control and monitor a full heat cycle. If E4 recurs, contact a technician to check blower performance and heat exchanger condition.