Furnace shows E10, indicating a communication error between the main Danfoss controller and a remote module (e.g., burner control or user interface)

Safety first: Disconnect power before handling communication wiring.

Steps:

• Check bus connections: Locate the communication terminals (often labeled A/B, +/−, or BUS) on the Danfoss controller and remote module. Ensure wires are firmly clamped and not shorted.
• Inspect cable: Follow the communication cable route and look for cuts, pinches, or signs of rodent damage. Replace damaged cable with the same type and shielding.
• Verify polarity and termination: Confirm that A connects to A and B to B between devices. Check that termination resistors are installed only where specified in the Danfoss documentation.
• Power-cycle devices: Restore power to both the main controller and remote module. Some communication faults clear after a full restart.
• Module substitution: If available, swap in a known-good remote module (e.g., burner control) to determine if the original is defective.