Lennox Furnace 311 Error Code — Meaning & Causes (2026)
Furnace heat firing rate has been reduced to match the available airflow (cutback mode). Below: what triggers it and what to check — this code carries no single repair to price. Reviewed July 2026.
What 311 means
Furnace heat firing rate has been reduced to match the available airflow (cutback mode).
Likely causes, most common first
- Dirty air filter
- Restrictive or undersized duct system
Base: 1 published national repair-cost guide (retrieved 2026-07) · full source registry on the methodology page · Code meaning & causes · Reviewed July 2026
No single repair to price for this code
311 doesn't point at one failed component, so we don't attach a price module — forcing a repair mapping here would be dishonest. If the code keeps returning, the underlying symptom (not the code) is what gets priced: browse the gas furnace repair costs for the problem you're actually seeing.
Codes are universal — your location changes the repair price, never the code's meaning. See the methodology for the exact localization formula and sources.
Reviewed by a Red Seal–certified appliance technician who also holds a Technical Safety BC gas ticket (Gas-C) and an ODS/halocarbon refrigerant ticket (CFC/HCFC/HFC).