🔥Furnaces Error Codes
Residential gas and electric furnace error and flash codes. Ignition lockouts, flame-sensor faults, pressure-switch and limit errors, and the parts that fix them across Carrier, Goodman, Lennox, Trane, Rheem and York. Gas and combustion work is flagged pro-recommended.
137 guides · Top brands: Carrier, Goodman, Lennox, Trane, Rheem, York
Section editor: James Rutherford · Master Plumber
Most Common Furnaces Fixes
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Furnace Error Code Lookup Tool: All Brands
Master furnace error code lookup guide covering Carrier, Goodman, Lennox, Trane, York, Rheem, Bryant, Heil, Amana, Coleman, and more.
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Carrier 13 Error Code — Limit Switch Lockout Fix
Carrier error code 13 means the limit switch tripped due to overheating. This guide covers every cause and fix — from clogged filters to cracked heat exchangers.
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Carrier 21 Error Code — Gas Heating Lockout Fix
Carrier error code 21 signals a gas heating lockout — the furnace failed to ignite after multiple attempts. Learn the exact steps to diagnose and reset it.
Recent Furnaces Guides
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Rheem Furnace Blower Won't Shut Off - Causes & Fix
Usually the thermostat fan switch is set to ON instead of AUTO, or there's a shorted wire between R and G creating a constant fan call.
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Rheem Furnace Igniter Not Working - Causes & Fix
Most often the igniter element has cracked or failed open. Test it with a multimeter at the leads for continuity and replace if open.
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Rheem Furnace Blowing Cold Air - Causes & Fix
Most often the thermostat fan is set to ON instead of AUTO, running the blower constantly with no heat call. Switch to AUTO first.
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Rheem Furnace Won't Turn On - Causes & Fix
Most often a dirty flame sensor or air filter causing the unit to lock out on ignition failure, flame loss, or limit trip.
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Rheem Furnace Not Heating - Causes & Fix
A dirty flame sensor is the most common cause. Clean the sensor rod with fine steel wool or emery cloth and verify the gas valve is open.
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Trane Furnace Igniter Not Working - Causes & Fix
Usually a cracked or failed hot-surface igniter. Less often, bad wiring, a faulty control board, or a gas valve issue prevents ignition.
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Trane Furnace Blowing Cold Air - Causes & Fix
Usually the thermostat fan is set to On instead of Auto, so the blower runs non-stop even when burners are off. Switch to Auto.
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Trane Furnace Short Cycling - Causes & Fix
Short cycling usually means a dirty air filter is blocking airflow and tripping the limit switch. Replace the filter first.
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Trane Furnace Not Heating - Causes & Fix
Most often a dirty filter blocking airflow or a thermostat set wrong. Check power, filter, gas supply, and read the blink code.
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Trane Furnace Won't Turn On - Causes & Fix
Usually caused by a thermostat set incorrectly, dead batteries, or a tripped breaker. Check power and settings first.
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Lennox Furnace Short Cycling - Causes & Fix
Short cycling is usually caused by a dirty air filter restricting airflow. Replace the filter and check that all vents are open.
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Lennox Furnace Blowing Cold Air - Causes & Fix
Usually caused by thermostat fan set to ON instead of AUTO, or a dirty filter blocking airflow. Switch fan to AUTO and replace filter.
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