Atwood Furnace: “3 flashes”
warning RV furnace fault codes
What it means
Three LED flashes followed by a 3-second pause, repeating. Indicates an ignition lockout fault: the board tried to light the burner (typically three tries) and failed, so it locked out. This is a soft lockout with roughly a one-hour timed retry, meaning the board may attempt ignition again on its own after the timeout.
Most likely causes
- Out of propane, propane valve closed, or air in the gas lines after running the tank low most likely
- Dirty or misadjusted igniter/flame electrode, or bad electrode gap, so no flame is established common
- Low gas pressure or partially blocked burner orifice / spider or insect obstruction in the burner tube common
- Faulty gas valve, igniter, or low 12V supply causing weak spark less common
Safe checks you can do yourself
- Confirm the propane tank has fuel and the valve is open; after refilling, the system may need a few ignition attempts to purge air from the line.
- Verify a healthy 12V battery/converter supply, since weak voltage produces weak spark.
- With power off, inspect the igniter/flame electrode for soot, corrosion, or bad position, and check the burner tube for obstructions (e.g. insect nests).
- Reset and watch a full ignition cycle to see whether spark, gas, and flame all occur.
How to reset / clear 3 flashes
- Turn the wall thermostat off and the setpoint all the way down; wait for the blower to stop.
- Either wait out the approximately one-hour timed soft-lockout for an automatic retry, or force an immediate reset by removing 12V power from the furnace for about 30 seconds.
- Restore power, turn the thermostat back on, and raise the setpoint to call for heat.
When to call a technician
Call a technician if the 3-flash code persists after confirming propane supply, healthy voltage, and a clean/properly positioned electrode, or if you are not comfortable working around the gas valve and burner. Persistent no-ignition may indicate a faulty gas valve, igniter, or control board.
Applies to
AFMD16 · AFMD20 · AFMD25 · AFMD30 · AFMD35 · Atwood Hydroflame AFM/AFMD series furnaces with the standard 3-tries-for-ignition diagnostic control board
FAQ
What does Atwood Furnace code "3 flashes" mean?
Three LED flashes followed by a 3-second pause, repeating. Indicates an ignition lockout fault: the board tried to light the burner (typically three tries) and failed, so it locked out. This is a soft lockout with roughly a one-hour timed retry, meaning the board may attempt ignition again on its own after the timeout.
How do I reset Atwood Furnace 3 flashes?
Turn the wall thermostat off and the setpoint all the way down; wait for the blower to stop. Either wait out the approximately one-hour timed soft-lockout for an automatic retry, or force an immediate reset by removing 12V power from the furnace for about 30 seconds. Restore power, turn the thermostat back on, and raise the setpoint to call for heat.
What is the most common cause of 3 flashes on a Atwood Furnace?
The most likely cause is out of propane, propane valve closed, or air in the gas lines after running the tank low.
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Sources
- Dometic (Atwood) Furnace Model AFM, AFMD Series Operating Instructions — Ignition Control Diagnostic Codes chart: 'Ignition Lockout Fault - 3-Flashes With 3-Second Pause - Soft (1 hr.)' (Forest River, Inc. (OEM-hosted manufacturer document))
- Atwood Shop/Service Manual - HydroFlame (2-stage furnace diagnostics section) — Sequence of operation/limit-switch section: control will 'lock out (three try for ignition, one hour lockout and then three retry)'; diagnostic chart defines LED flash codes (Atwood Mobile Products (service manual hosted by My RV Works))
Note: The roughly one-hour timed retry ('three try, one-hour lockout, then three retry') is described in the Atwood service literature; exact retry counts and timing can vary slightly by board revision and by single-stage vs two-stage controls. The 3-flash ignition-lockout code is distinct from the 2-flash flame-sense hard lockout.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.