Lennox Furnace error codes

16 verified Lennox furnace error codes — plain-English meanings, likely causes and safe step-by-step fixes for each.

LED off LED on (solid) Slow heartbeat Fast heartbeat 1 2 3 4 5 7 8 9 10 11 12 13

Before you start

Write down the exact code on the display, including any letters. Many codes clear after a power reset: unplug the appliance for 2–3 minutes, plug it back in, and run a short cycle. If the code comes back, open its page below and work through the fixes in order.

All Lennox error codes → · Furnace codes across all brands →