What is your furnace trying to tell you?
Look up a furnace error or flash code and get the meaning, likely causes, safe checks, and when to call a pro, from the manufacturer's own manual.
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Pick your furnace brand to see every code we cover.
Featured codes
A sample of codes from each brand.
Ignition lockout: system failed to ignite gas and prove flame in 4 attempts. Control auto-resets after 3 hours (see code 34).
Limit circuit lockout: a limit or flame rollout switch was open longer than 3 minutes. Control auto-resets after 3 hours (see code 33).
Grounding fault / poor neutral connection.
Open rollout switch.
Improper main ground, OR line voltage below 90 volts. Control will not respond to a heat call until voltage rises above 95 volts.
Watchguard 1 hour: burners failed to ignite or lost flame 5 times during a single heating demand.
One-hour lockout, caused by repeated failed ignition (11), water sensed (59), dead blower (61), internal fault (93), flame lost 5 times (13) or unexpected flame (14).
Flame present with gas valve off. Extremely critical; furnace will not operate.
Loss of the IRQ or other internal failures (internal furnace control error).
Why you can trust these pages
How we put each code page together.
From the manual
Every meaning and cause comes from the manufacturer's installation or service manual, and each page links to its source.
Nothing guessed
If we could not confirm a code in a manual, we left it out instead of guessing.
Safety first
Each page separates simple homeowner checks from work that needs a licensed HVAC technician.