Atwood Furnace Ignition Lockout Fault 3 Flashes With 3-Second Pause

The Atwood furnace ignition lockout fault indicated by 3 LED flashes followed by a 3-second pause is a common diagnostic code seen in RV and mobile-home furnaces. This article explains causes, diagnostic steps, safety considerations, and repair options to help users identify the problem and decide between DIY fixes and professional service.

Symptom	Likely Cause	Recommended Action
3 LED Flashes, 3-Second Pause	Ignition Lockout (failed ignition sequence)	Check gas supply, electrode gap, wiring, flame sensor, control board
Repeated Cycling/No Heat	Intermittent ignition, weak spark, contaminated or bent sensor	Clean/adjust electrode, inspect wiring, test gas valve

What The 3 Flashes With 3-Second Pause Means

On many Atwood and Dometic furnace control boards, the LED flash pattern is a diagnostic language. Three flashes followed by a 3-second pause typically means the controller attempted ignition multiple times but entered an ignition lockout after failing to establish a flame.

Ignition lockout is a protective feature that prevents continuous gas flow when ignition is unreliable, reducing risk of unburned gas accumulation and potential fire or explosion.

Common Causes Of Ignition Lockout

Gas Supply Problems

Insufficient propane or natural gas pressure, an empty tank, closed valve, clogged line, or an activated regulator can prevent sufficient gas flow for ignition. Low-pressure conditions can produce weak or no flame.

Ignition Electrode Issues

Electrodes (spark ignitors) can become fouled with soot, misaligned, cracked, or worn. A weak or absent spark prevents the burner from lighting even if gas is present.

Flame Sensor Or Thermocouple Faults

The flame sensor or thermocouple detects flame presence. If it is dirty, mispositioned, or failed, the control board will not see flame and will shut down after ignition attempts.

Control Board Or Wiring Faults

Damaged wiring, loose connectors, short circuits, or a failing control board can interrupt signals during ignition. Corrosion in terminals and connectors is common in mobile environments.

Gas Valve Or Solenoid Failure

The gas valve or its solenoid may fail to open or may open inconsistently. Mechanical sticking or internal electrical faults can prevent proper gas flow during the ignition window.

Blocked Burner Or Venting Issues

A clogged burner port, insect nest, lint buildup, or restricted ventilation can prevent proper combustion. A blocked flue can cause draft problems that extinguish or prevent a flame.

Safety Precautions Before Troubleshooting

Always start with safety: turn off the furnace power and gas supply before accessing components. Work in a well-ventilated area and avoid open flames while inspecting the gas system.

For those unfamiliar with gas appliances, electrical systems, or soldered wiring, it’s safer to contact a licensed RV technician or HVAC professional. Improper repairs can cause gas leaks, fire, or carbon monoxide hazards.

Step-By-Step Diagnostic Checklist

1. Verify Gas Supply

Confirm propane or natural gas tank has fuel and valves are fully open. Check the regulator for frost or damage and ensure supply lines are free of kinks. If another appliance on the same system works, supply is likely good.

2. Power And Fuse Check

Ensure the furnace has 12V DC power and the fuse or breaker for the furnace is intact. Replace any blown inline fuses and confirm battery systems if used in an RV.

3. Observe Ignition Sequence

Turn on the furnace and watch the ignition attempt. Listen for the click of the ignitor, smell for gas, and note any delayed or weak spark. The LED code will help pinpoint which phase failed.

4. Inspect And Clean Electrodes

Remove access panels to reach the electrode and flame sensor. Clean electrode tips gently with fine emery cloth or steel wool to remove carbon build-up. Confirm electrode gap and alignment to manufacturer specifications.

5. Examine Flame Sensor/Thermocouple

Clean the sensor rod and ensure it sits correctly in the flame path. A weak reading can be caused by soot or improper position. Replace if evidence of corrosion or mechanical damage exists.

6. Check Wiring And Connectors

Inspect all wiring harnesses for chafing, corrosion, or loose pins. Wiggle each connector while observing the LED; intermittent contacts may reproduce the fault. Tighten or replace terminals as needed.

7. Test Gas Valve Function

With safety in mind, verify the gas valve energizes when the controller commands ignition. Use a multimeter to check for expected voltage at the solenoid during the ignition attempt. If voltage is present but valve doesn’t open, replace the valve.

8. Clean Burner And Venting

Remove debris, spider webs, or lint from burner ports and flue. Confirm exhaust exit is unobstructed. A clean burner and correct draft are essential for stable ignition and flame sensing.

How To Measure And Adjust Electrode Gap

Electrode and sensor positioning is critical. Refer to the furnace manual for the exact gap specification. A commonly used gap is about 1/8 inch (3 mm), but models vary.

To set the gap, loosen the mounting screws, position the electrode using a non-conductive tool, then tighten and recheck. Avoid bending the rod repeatedly to prevent metal fatigue.

Using A Multimeter For Electrical Diagnostics

A digital multimeter helps check continuity, voltage, and resistance. Measure 12V supply to the control board, verify voltage at the ignitor and gas valve during ignition attempts, and check continuity across safety switches.

If the expected voltage is absent at the valve or ignitor, trace back to connectors and the control board. If voltage is present but the component fails, that component is likely defective.

When To Replace Parts

Replace the ignition electrode if it shows cracks, heavy pitting, or no spark despite correct wiring and voltage. Replace flame sensors if cleaning doesn’t restore reliable flame detection.

Gas valves should be replaced if they do not respond to the control signal or if internal leaks are suspected. Control boards are replaced when diagnostics show correct inputs but no command outputs or erratic behavior.

Common Replacement Part Numbers And Sources

Atwood and Dometic furnaces share many components. Use the furnace model number to find exact part numbers for ignitors, flame sensors, control boards, and gas valves.

Genuine OEM parts are recommended for safety and reliability. Parts can be sourced from RV parts suppliers, authorized dealers, or reputable online retailers. Verify compatibility against the furnace serial/model tags.

DIY Versus Professional Repair

Routine cleaning, visual inspection, and simple electrode adjustments are suitable DIY tasks for someone comfortable with basic tools and safety practices.

Complex diagnostics involving gas valve replacement, control-board swapping, or leak testing should be handled by a licensed technician. HVAC or RV service pros will have leak-detection tools, manifold gauges, and the technical manuals required for safe repair.

Preventive Maintenance To Avoid Lockouts

• Regular Cleaning: Clean burner assembly, electrodes, and sensors yearly or as recommended.
• Annual Inspection: Have a qualified technician inspect seals, gas lines, and controls annually.
• Use Fuel Filters: Install or replace inline fuel filters if the system supports them to prevent debris in the gas valve.
• Protect From Moisture: Keep access compartments dry to reduce corrosion of electrical connectors.

Troubleshooting Quick-Reference Checklist

Step	Action
1	Confirm fuel supply and open valves
2	Verify 12V power and fuses
3	Observe ignition clicks and LED code
4	Clean/align electrodes and sensors
5	Inspect wiring and connectors
6	Test gas valve operation and replace if needed

When The Problem Persists

If the furnace continues to display 3 flashes with a 3-second pause after completing the checklist, document observations: whether the ignitor clicks, if gas odor is present, and any intermittent behavior.

Provide this information to a service technician. Detailed notes accelerate diagnostics and reduce repair cost by narrowing likely failure points.

Useful Resources And Manuals

Manufacturer manuals, technical service bulletins (TSBs), and OEM wiring diagrams are invaluable. Search for the furnace model number followed by “service manual” or consult the Atwood/Dometic support site for downloadable PDFs.

RV forums and owner communities can provide model-specific tips and part recommendations, but rely on official manuals for safety-critical procedures.

Key Takeaways

The 3-flash, 3-second pause code signifies ignition lockout, a safety response to failed ignition attempts. Diagnosing requires a methodical check of fuel supply, ignitor, flame sensor, wiring, gas valve, and venting.

Minor cleaning and adjustment can fix many lockout issues, but gas valve, sensor, and control-board faults often need replacement. When in doubt, prioritize safety and consult a qualified technician.

Note: This article provides general guidance and is not a substitute for professional repair or the furnace manufacturer’s service instructions.