Lennox: Open High-Limit Switch
What this fault means
The high-limit opened on excess temperature — an airflow fault that shortens heat-exchanger life if left unaddressed.
Likely causes
- Dirty filter
- Blocked registers or ductwork
- Blower or capacitor failure
What you can safely check
- Replace a dirty air filter — restricted airflow causes a surprising share of furnace faults.
- Confirm registers and the outdoor unit are clear of snow, leaves and debris.
- Cycle power at the switch once and let the system retry.
Call a technician — don't keep resetting this
Open High-Limit Switch is a high-severity fault. Repeated resets of a safety lockout can mask a serious problem such as a cracked heat exchanger (a carbon-monoxide risk) or a failing compressor. If you smell gas, leave and call FortisBC at 1-800-663-9911 or 911 first.
Related Lennox faults
Lennox furnace showing Open High-Limit Switch?
CANRO Heating & Cooling — same-day diagnosis across Greater Vancouver. Call 604-359-1081.