E438
Lennox Internal Control Board Fault (Communicating System)

Thermostat displays E438; furnace may not respond to thermostat commands or may operate erratically.

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Safety Warning

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.

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Possible Causes

Failed Lennox integrated furnace control, Corrupted firmware, Surge or lightning damage, Intermittent internal relay failure

How to Fix / Troubleshooting

Safety: Turn off power before touching the control board.

  • 1. Power reset: Turn off the furnace breaker for 5 minutes, then restore power to clear transient faults.
  • 2. Inspect board: Remove blower door and visually inspect the Lennox control board for burn marks, swollen components, or corrosion.
  • 3. Check connections: Ensure all multi-pin connectors are fully seated and that no wires are loose or pinched.

If E438 persists after a reset and wiring check, the control board likely needs replacement by a qualified technician, who can also verify correct programming for your Lennox model.

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Repair Difficulty

Professional Required 5/5

Required Part

Lennox Integrated Furnace Control Board
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