Keep the furnace off. Do not reset a rollout switch. If you smell gas or a carbon-monoxide alarm sounds, leave the building and contact emergency services or the gas utility.
What does Lennox code 200 mean?
Lennox furnace code 200 means the rollout circuit is open, or had opened, and the furnace is in hard lockout on the supported control family. Confirm the model number and diagnostic chart inside the furnace door before replacing parts.
What causes Lennox code 200?
- A blocked flue or combustion-air path
- A burner or gas-pressure problem
- A damaged or restricted heat exchanger
Can I troubleshoot Lennox code 200?
Keep the furnace off. Do not reset a rollout switch. If you smell gas or a carbon-monoxide alarm sounds, leave the building and contact emergency services or the gas utility.
How much does Lennox code 200 cost to fix?
A heat exchanger replacement typically costs between $500 and $3,500 nationally.
When should I call a technician?
Leave the furnace off and call a licensed technician for a combustion-safety inspection.
Symptoms this code causes
Sources and model scope
Fault codes vary by model and control board. Confirm the diagnostic chart inside your furnace panel or the official manual before acting.
Scope used here: Lennox integrated controls covered by installation instructions 508001-02D.
- Lennox Industries: Installation Instructions — Integrated Control Diagnostic Codes
508001-02D · Lennox furnaces explicitly covered by installation instructions 508001-02D; not a universal Lennox code list.
Compiled by Warmlo Editorial · Reviewed August 2026
This is general information, not professional advice. Gas, electrical, and combustion repairs can be dangerous — when in doubt, call a licensed technician.