Why does my Atwood furnace ignite but then shut off after a few seconds?

This is most commonly caused by a dirty or failing flame sensor (sail switch) that cannot detect the flame properly. The control board initiates a safety lockout when it doesn't receive confirmation that the burner is lit. Clean the flame sensor with fine emery cloth or replace it if cleaning doesn't resolve the issue.

Can a weak or low propane supply cause my Atwood furnace to not stay lit?

Yes, insufficient propane pressure or a nearly empty tank can cause the furnace to light briefly and then go out. Check that your propane tank has adequate fuel and that the regulator is delivering the correct pressure (typically 11 inches of water column). Also inspect the gas line for kinks, blockages, or a stuck gas valve that may be restricting flow.

Could a faulty sail switch be the reason my Atwood furnace won't stay lit?

Absolutely. The sail switch detects airflow from the blower motor, and if it is stuck, misaligned, or defective, it can signal the control board to shut down the gas valve prematurely. Test the sail switch for continuity with a multimeter when the blower is running. If it fails to close properly, replace it to restore normal furnace operation.

How does a dirty or obstructed exhaust vent affect my Atwood furnace staying lit?

A blocked exhaust vent or intake tube can cause improper combustion and trigger the furnace to shut down as a safety precaution. Insects, mud dauber nests, and debris commonly obstruct RV furnace vents, especially after periods of storage. Inspect and clean both the intake and exhaust tubes thoroughly, and consider installing vent screens to prevent future blockages.

Can a bad control board cause my Atwood furnace to cycle off shortly after igniting?

Yes, a malfunctioning Atwood control board (also called the circuit board or ignition module) can incorrectly interpret sensor signals and shut the furnace down even when the flame is burning properly. If you've already ruled out the sail switch, flame sensor, gas supply, and airflow obstructions, the control board is likely the culprit. Replace it with the correct Atwood-compatible board and verify all wiring connections are secure during installation.

Atwood Furnace Won't Stay Lit — RV Diagnostic Guide

Probable Causes

Dirty or failed sail switch — the most common cause on Atwood furnaces. The sail switch confirms airflow before allowing the gas valve to open and must remain closed to keep the burner running.
Weak or dead blower motor — insufficient airflow fails to hold the sail switch closed.
Dirty flame sensor / igniter (hot surface igniter or electrode) — the control board can't confirm flame presence and shuts down the gas valve.
Faulty circuit board (Fenwal or Dinosaur replacement) — the board's flame-sensing circuit may be intermittent or failed.
Obstructed intake or exhaust vents — mud dauber nests, debris, or a kinked exhaust tube restricts airflow, triggering safety shutdown.
Low LP gas pressure — weak supply pressure causes a marginal flame the board interprets as a flame-out.
Loose or corroded wiring connections — vibration from travel loosens spade connectors at the board, sail switch, or gas valve.

Urgency & Safety

High priority. An Atwood furnace that lights then shuts down can indicate incomplete combustion or gas flow issues. Never bypass any safety switch. If you smell propane at any point, shut off the LP tank immediately, ventilate the RV, and do not operate any electrical switches. Carbon monoxide is also a concern — ensure your CO detector is functioning before troubleshooting.

DIY Difficulty

Moderate (5/10). Most diagnosis requires a multimeter, basic hand tools, and comfort working around LP gas components. The furnace must be removed from its compartment for full access on most Atwood models.

Typical Repair Cost

| Repair | DIY Cost | Shop Cost | |---|---|---| | Sail switch replacement | $15–$30 | $100–$175 | | Circuit board replacement | $50–$120 | $175–$300 | | Blower motor replacement | $80–$150 | $250–$400 | | Full cleaning & tune-up | $10 (supplies) | $125–$200 |

Parts You May Need

Sail switch (Atwood 36680 or model-specific equivalent)
Replacement circuit board (Dinosaur UIB-S or Fenwal OEM)
Blower motor (match your model number, e.g., Hydro Flame 8500 series)
Hot surface igniter or electrode (model-specific)
Fine-grit sandpaper or emery cloth for electrode cleaning
Compressed air for vent/burner cleaning

Step-by-Step Diagnosis

Verify LP supply. Confirm the tank is at least 20% full and the valve is fully open. Run another LP appliance (stovetop) to confirm adequate gas pressure and flow.
Inspect the vents externally. Look into the furnace intake and exhaust tubes on the outside of the RV. Remove any insect nests, leaves, or debris. A blocked exhaust is a very common cause.
Remove the furnace access panel. Power off the furnace at the thermostat. Disconnect shore power or the battery if you'll be handling wiring.
Check wiring connections. Inspect every spade connector on the circuit board, sail switch, gas valve, and blower motor. Push each one firmly onto its terminal. Look for green corrosion or melted insulation.
Test the sail switch. Reconnect power, set the thermostat to call for heat, and listen for the blower to start. With the blower running, use a multimeter set to continuity across the sail switch terminals — it should read closed (near 0 ohms). If it reads open with the blower running, replace the sail switch.
Inspect the igniter/electrode. Lightly sand the flame sensor electrode with emery cloth to remove carbon buildup. Check the gap (typically 1/8"). A glazed or cracked hot surface igniter should be replaced.
Observe the ignition sequence. Restore power, call for heat, and watch. The blower should start → sail switch closes → board energizes igniter → gas valve opens → flame lights. Note exactly where the sequence fails or where the flame lights then dies. If the flame lights and the board still shuts down within 15–30 seconds, the flame sensor circuit or the board itself is likely the problem.
Test the circuit board. With flame present, measure DC voltage between the flame-sense terminal and ground on the board. If the board is not recognizing the flame despite a clean sensor and good connections, replace the board.

When to Call a Technician

Call a certified RV LP gas technician if you smell gas and cannot identify the source, if the furnace repeatedly locks out after your cleaning and component checks, if you need to measure or adjust gas manifold pressure (requires a manometer), or if you're uncomfortable pulling and reinstalling the furnace unit. Gas system work done incorrectly can cause fire or carbon monoxide poisoning — there's no shame in handing this one off.

Atwood Furnace Won't Stay Lit

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