Atwood Furnace: “Steady on (no flash)”
danger RV furnace fault codes
What it means
The diagnostic LED on the ignition control board is on continuously with no flashing, indicating an internal circuit board failure. This is a hard lockout: the furnace will not run until the board is reset (and, if the fault repeats, the board itself is likely faulty).
Most likely causes
- Failed or faulty ignition control / circuit board most likely
- Low or unstable 12V DC supply voltage to the board (weak battery, corroded connections, undersized wiring) common
- Loose, corroded, or reversed power/ground connections at the board common
- Moisture or pest/wiring damage on the board less common
Safe checks you can do yourself
- Confirm the furnace has a strong 12V DC supply: check battery state of charge and that the converter is working; Atwood boards misbehave below roughly 10.5-11V.
- Inspect the furnace power and ground connections for looseness, corrosion, or chafed wires; clean and re-seat connectors with power off.
- Try a single reset (thermostat off, then 12V power removed for ~30 seconds, then restored). If the steady light returns immediately, stop and have the board diagnosed.
How to reset / clear Steady on (no flash)
- Turn the wall thermostat off and turn the temperature setting all the way down.
- Wait for the blower fan to stop.
- Remove 12V DC power from the furnace (switch off the furnace circuit or disconnect the fuse) 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 qualified RV technician if the LED stays steady-on after a proper power-cycle reset, or if you are not comfortable verifying 12V supply and connections. A persistent internal-board-failure indication generally means the control board needs professional diagnosis or replacement.
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 "Steady on (no flash)" mean?
The diagnostic LED on the ignition control board is on continuously with no flashing, indicating an internal circuit board failure. This is a hard lockout: the furnace will not run until the board is reset (and, if the fault repeats, the board itself is likely faulty).
How do I reset Atwood Furnace Steady on (no flash)?
Turn the wall thermostat off and turn the temperature setting all the way down. Wait for the blower fan to stop. Remove 12V DC power from the furnace (switch off the furnace circuit or disconnect the fuse) 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 Steady on (no flash) on a Atwood Furnace?
The most likely cause is failed or faulty ignition control / circuit board.
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Sources
- Dometic (Atwood) Furnace Model AFM, AFMD Series Operating Instructions — Ignition Control Diagnostic Codes chart (Standard 3 Tries for Ignition Controls): 'Internal Circuit Board Failure - Steady On, No Flashing - Hard' lockout (Forest River, Inc. (OEM-hosted manufacturer document))
- Atwood Furnace AFM Operating/Service Manual — Ignition Control Diagnostic Codes: Internal Circuit Board Failure = Steady On, No Flashing, Hard lockout; covers models AFMD16/20/25/30/35 (Atwood Mobile Products (manual hosted at Heartland Owners manuals library))
Note: Code applies to the single-stage 'standard 3 tries for ignition' Atwood/Dometic AFM/AFMD control board. Two-stage boards use a similar but separate chart. A steady-on light can sometimes also reflect a power/voltage problem rather than a truly dead board, so verify supply voltage before condemning the board.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.