Furnace Fault Codes

Furnace flashing 3 times: what 3 flashes means

The number of flashes on a furnace control board is not a standard. Every manufacturer assigns its own meanings, and 3 flashes means something different across the 8 control families below.

On an Armstrong it is burner failed to light, or lost flame during a heat demand, on a Goodman it is pressure switch will not close, and on a Heil it is low pressure switch still open 30 seconds after the inducer started.

None of those three are the same underlying issue — three flashes points to three unrelated faults depending on the brand, and the count itself won't sort them out. Manufacturer first, action second.

Some of the faults listed here are gas-safety faults. Those ones involve the gas valve, the burner compartment, or the heat exchanger — the parts whose failure can put combustion products, including carbon monoxide, into the air the house breathes, and each carries this warning on its own page. Do not keep resetting a furnace that reports one of them in order to hold the heat on. Have it looked at by a licensed technician, and make sure there is a working carbon monoxide alarm on every level of the home, including the level the furnace is on. The conditions that mean stop now.

3 flashes, by manufacturer

Furnace brandWhat 3 means there
Armstrong
3 flashes		Burner failed to light, or lost flame during a heat demand
Goodman
3 flashes — Goodman GMS, GMP, GMH, GMV8, GMV9 and Amana AMH, AMV9 series		Pressure switch will not close
Goodman
3 red flashes — GMEC96 / AMEC96		First stage pressure switch stuck open, or an inducer error
Goodman
3 amber flashes — GMEC96 / AMEC96		Second stage heat called with no first stage call
Heil
3 flashes		Low pressure switch still open 30 seconds after the inducer started
Rheem
*RC 92+ / *RL 90+		Pressure switch closed when it should be open
Rheem
Rheem standard gas furnaces		Limit switch open
Trane
3 flashes		Draft pressure error
York
3 red flashes — UTEC / ST		Pressure switch open, or first stage pressure switch open
York
3 amber flashes — UTEC / ST		Second stage heat present with no first stage call

Before counting again

If the light blinks evenly with no break at all — nothing like the three-count grouping on this page — that's a heartbeat signal, not a code: the board is simply powered and has nothing wrong to flag. See how each brand marks normal operation.

Finding out which brand you have

Look inside the cabinet for the rating plate — that's where the actual brand is listed, since many furnaces carry a badge name that differs from their control board's manufacturer, and the thermostat won't help either. If your display shows a number instead of blinking, reading a furnace fault code explains both that and where to find the plate.

Other flash counts

What the fix costs

When the failed part turns out to be the board itself, this page on control board replacement cost has the typical range; for other parts, or just the service call, the general repair cost guide has that instead.

What 3 flashes usually points to

3 flashes keeps the pressure-switch theme from 2 flashes but reverses the failure: Goodman, Heil, Rheem's *RC/*RL board and York all report the switch stuck open, or an inducer that is not building draft, rather than stuck closed. Armstrong instead uses 3 flashes for a burner that failed to light or lost flame mid-cycle. Worth checking first: the pressure switch tubing for a kink, disconnect or blockage, and the vent and intake pipes for anything restricting airflow. Where 2 flashes usually means a stuck-closed switch, 3 flashes more often traces back to the venting or the inducer motor behind it.

Sources

Every three-flash reading on this page is sourced to the manufacturer document referenced from its code page:

This site is a reference, not a substitute for a licensed HVAC technician. Gas appliances can leak carbon monoxide and cause fire. Anything involving gas lines, the heat exchanger, or the flame sensing circuit should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.