Furnace Repair Glossary

Plain-English explainers for the technical terms, rebates, regulations, and acronyms that show up when you shop for Furnace Repair systems and services. Each entry links the underlying source, lists the numbers that matter, and points to related concepts.

Carbon Monoxide (CO)
The odorless, colorless gas a failing furnace can leak — the reason furnace safety is a health issue, not just a comfort one.
Combustion Analysis
The instrumented test that proves a furnace is burning safely and efficiently — the difference between a real tune-up and a look-over.
Condensing Furnace
A 90%+ efficient furnace with a second heat exchanger — and a condensate drain whose clog is a surprisingly common no-heat cause.
Draft Inducer Motor
The small fan that clears combustion gases out the flue before the burners fire — when it fails, the furnace safely refuses to start.
Flame Sensor
The metal rod that proves the burners actually lit — a dirty one is the single most common reason a furnace short-cycles into no heat.
Furnace Gas Valve
The electrically controlled valve that meters and shuts off gas to the burners — a core safety part with a wide repair-cost range.
Heat Exchanger
The metal chamber that separates combustion gases from the air you breathe — and the one furnace failure that's a safety issue, not a fix.
High-Limit Switch
The overheat cutoff that protects the heat exchanger — when it trips, the fix is usually airflow, not the switch itself.
Hot Surface Igniter (HSI)
The glow-element that lights the burners on a modern furnace — brittle, cheap, and the most common reason a furnace won't fire.
Ignition Control Board
The furnace's circuit-board brain — it sequences ignition, the inducer, the blower, and every safety check, and stores the fault codes.
Pressure Switch
The safety switch that won't let the furnace fire until venting is proven — and it often trips because of a clog, not its own failure.
Thermocouple
The pilot-light safety sensor on older furnaces — the standing-pilot ancestor of today's flame sensor, and a cheap, common fix.
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