Furnace guides
Answers to common gas furnace questions, based on manufacturer manuals and government safety and energy sources.
Furnace Air Filters: How Often to Change and Why It Matters
How a dirty furnace filter causes limit and short-cycling faults, how often to check it, and what MERV ratings mean.
Furnace Blowing Cold Air: Common Causes
Why a gas furnace blows cold or room-temperature air, from thermostat fan settings to limit and ignition faults, and what to check.
Furnace Flame Sensor: Symptoms, Codes and Cleaning
What a furnace flame sensor does, the codes that point to it, what the manuals say about cleaning it, and safety cautions.
Furnace Pressure Switch Error: What It Means
What a gas furnace pressure switch does, common pressure switch codes by brand, likely causes from the manuals and what to check.
Furnace Repair or Replace: How to Decide
Factors to weigh when deciding whether to repair or replace a gas furnace, based on U.S. Department of Energy and ENERGY STAR guidance.
Furnace Short Cycling: Causes and What to Check
Why a gas furnace turns on and off too often, the fault codes that often go with it, and safe checks before calling a technician.
How to Read a Furnace LED Flash Code
How to find and read the blinking LED or display code on a gas furnace control board, with brand-by-brand examples from the manuals.
How to Reset a Gas Furnace Safely
When and how to reset a gas furnace after a lockout, what the manuals say about automatic resets, and when not to reset.
Why Is My Furnace Blinking a Code?
What a blinking light on your furnace means, which faults are most often behind it, and what you can safely check yourself.