Next Phase Heating is an independent HVAC contractor. We are not an authorized dealer for, or affiliated with, any equipment manufacturer. Brand names are used only to identify the equipment we service.
Gas furnaces
Goodman & Amana
Three different diagnostic systems, and a control board that sits upside down in half of all installs.
Carrier & Bryant
Short flashes then long flashes. Read them the wrong way round and 13 becomes 31, which is a different fault entirely.
Trane & American Standard
Flame rollout has no code of its own here. It reads as four flashes, which looks like a dirty filter.
Rheem & Ruud
Not flashes at all — a two-digit display, one digit at a time. Most Rheem articles online describe the wrong system.
Lennox
Four systems, and on one model the rollout flash count changed between manual revisions. The brand where the wrong chart costs most.
Ductless mini splits
Mitsubishi Electric
Blink counts, not codes — and the same count means two different things depending on the mode the unit is in.
Daikin
The light is only a flag. The code has to be pulled out with the remote, and some codes never show up in the scroll list.
Before you count anything
Every one of these pages starts the same way, because the same mistake causes most of the confusion: work out which control your equipment has before you look up a number. Manufacturers change diagnostic systems between model years and do not always keep the numbering, so the first chart a search engine hands you may have been written for a different machine than the one in your garage. The legend printed on your own equipment always wins — on most furnaces it is on the wiring diagram inside the blower door.
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Quick answers
Why does the code chart I found not match my furnace?
Because manufacturers change their diagnostic systems and do not always keep the numbering. Goodman has used three different systems, Lennox four, and on one Lennox model the flash count for flame rollout moved between the 2021 and 2024 versions of the same manual. Match the model number on the door, not just the brand.
Is there an error code for a cracked heat exchanger?
No. No manufacturer builds one, because a control board cannot detect a crack. Rollout and repeated limit faults can be downstream signs of one, and they are a good reason to have the furnace inspected properly, but the crack itself is found with a camera and a combustion analyser rather than by a flashing light.
Can I reset my furnace and see if the code clears?
For a one-off ignition failure, once is reasonable. For anything involving flame rollout, or a flame detected when the gas valve should be closed, no. Those faults exist specifically to stop the appliance doing something it should not, and resetting past them repeatedly is the habit they are designed to interrupt.
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