Code 112 = Flame failure during operation. Burner lit but flame dropped out before draw ended. Distinct from Code 111 (no ignition).
Diagnostic sequence
1. Flame rod cleaning (#1 cause)
Carbon buildup over time. Cleaning resolves 60% of chronic Code 112 cases on units 5+ years old.
2. Vent restriction
Birds nest, ice, undersized vent. Inspect termination.
3. Condensate blockage (condensing models)
Blocked trap. Often paired with overheat code.
4. Gas pressure drop under load
Another gas appliance fires mid-draw, dropping pressure.
5. Heat exchanger scale
Changes burner dynamics. Run a descale.
Reset
- Clean flame rod
- Power cycle
- Monitor for 24 hours
Bottom line
Flame rod cleaning resolves most Code 112 cases on older units.