Furnace LED flashes code 31; inducer may run but ignition sequence does not complete. Often indicates pressure, draft, or venting problem.

Safety first: Turn off power before removing panels. Do not operate furnace with venting disconnected.

• Check outdoor terminations: Inspect the furnace intake and exhaust pipes outside for obstructions (snow, ice, leaves, nests). Clear any blockage carefully.
• Inspect pressure tubing: With power OFF, verify the rubber tubing from the inducer housing to the pressure switch is intact, not brittle, and firmly connected at both ends.
• Check for water in tubing: On condensing models, remove the tubing and check for water accumulation. Drain and dry if present, then reinstall.
• Reset and test: Restore power, call for heat, and observe whether the code clears and the furnace runs.

If code 31 persists, the vent system design, inducer performance, or pressure switch calibration may be at fault. A technician should measure draft and verify vent sizing per Day & Night installation instructions.