Furnace shows E17 and stops, indicating a safety chain or external interlock open

Safety first: Do not bypass safety devices. Identify and correct the cause of the open safety circuit.

Steps:

• Check access panels: Ensure all furnace doors and panels are properly closed so that door interlock switches are engaged.
• Inspect auxiliary limits: Look for manual-reset limit switches on the blower housing or near the burner. If a red reset button is present and popped, press it once to reset. Investigate why it tripped (overheating, blocked airflow).
• Verify external emergency stop: Confirm that any external emergency stop buttons or boiler room safety switches are in the RUN position.
• Trace safety wiring: Using the wiring diagram, follow the safety loop wiring from the Danfoss controller through all devices. Look for loose connections or broken wires.
• Reset and test: After restoring the safety loop, reset the controller and observe operation. If E17 recurs, a safety device may be intermittently opening and should be tested by a technician.