🔥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.
48 guides · Top brands: Carrier, Goodman, Lennox, Trane, Rheem, York
Section editor: Error Code Fixes Editorial Team ·
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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York Furnace Igniter Not Working - Causes & Fix
Usually a cracked igniter or dirty flame sensor causing ignition lockout. Check LED code, inspect igniter for cracks, and clean sensor.
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Lennox Furnace Igniter Not Working - Causes & Fix
Usually a cracked hot surface igniter that can't reach ignition temperature. Also check gas supply, flame sensor, and control board output.
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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 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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Goodman Furnace Igniter Not Working - Causes & Fix
The igniter is likely failed and not glowing when voltage is applied. Verify the igniter receives 115–120 VAC during ignition.
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Carrier Furnace Igniter Not Working - Causes & Fix
The igniter is worn out or has failed. A technician replaces the igniter and verifies the ignition sequence completes normally.
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Boiler vs. Furnace Replacement: Cost, Efficiency, and When to Switch
Boiler replacement costs $4,000–$8,000 vs. furnace $2,200–$5,500. Hydronic vs. forced air comparison, conversion costs, and efficiency pros and cons for Northeast and Midwest homes.
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Furnace Age Guide: When to Repair and When to Replace
Find your furnace age by serial number for Carrier, Trane, Lennox, Rheem, and Goodman. Age-based replacement rules with IRA tax credits for gas furnaces and heat pumps.
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Furnace Blowing Cold Air - 8 Causes and How to Fix Each
Your furnace is running but blowing cold air. Here are 8 causes from thermostat settings to a failed igniter, with step-by-step fixes for each.
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Furnace Won't Ignite - 7 Causes and How to Fix Each
Your furnace is calling for heat but the burner will not light. Here are 7 causes from a bad igniter to a blocked condensate line, with step-by-step fixes.
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Heat Pump vs. Gas Furnace: Total Cost Comparison and Decision Guide
Compare upfront costs, operating costs by region, climate suitability, IRA tax credits, and lifespan for heat pumps vs gas furnaces to make the right HVAC decision.
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