What is your furnace trying to tell you?

1. Count the flashes

Most furnaces blink an LED behind a small window in the lower door. Count the pattern — short and long flashes matter. Mini-splits show a code on the unit or remote.

2. Look it up by brand

The same count means different things on different brands. Every page here quotes the brand's own manual, so you are reading what the manufacturer says, not a guess.

3. Check the safe stuff first

Filters, vents, switches, and drain clogs fix a surprising share of codes. Anything past that is a job for a licensed technician — each page says which is which.