Armstrong Air communicating thermostat displays E5; furnace may not respond to staging commands.

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Loose low-voltage harness at furnace board, Damaged communication cable, Faulty furnace control module

Safety: Turn off power before unplugging any harnesses.

Steps to check:

Inspect control board connectors: Ensure all multi-pin plugs on the Armstrong Air integrated furnace control are fully seated.
Check thermostat cable: Look for damage or splices in the cable between thermostat and furnace.
Power cycle system: Turn off power for several minutes, then restore and observe if E5 clears.
Replace control module: If wiring is intact and E5 persists, the furnace control board may need replacement.

Hard 4/5

Integrated Furnace Control Board

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