Oct 24th 2026
Atwood / Dometic Water Heater Won’t Light: Lockout Light, Ignition Board and Fixes
TROUBLESHOOTING · GAS
Atwood / Dometic Water Heater Won’t Light: Lockout Light, Ignition Board and Fixes
Red light on the switch? The heater tried three times to light and locked out. Here’s why, in the order Atwood’s service manual checks it.
Check these first
- Reset: turn the switch OFF, then ON. If the light stays on longer than 15 seconds, turn it off, wait 5 minutes and try again.
- Propane on and the tank full? Air in the line after a tank change is common.
- 12V: Atwood wants at least 10.5 VDC (Dometic: 10–14 V). Check the 2 A fuse (never larger than 3 A).
- Gas pressure: 11 in. water column with appliances running, 13 in. max at the valve.
Covers these models
Atwood and Dometic RV water heaters with electronic (DSI) ignition. Models ending in “P” are pilot relight.
How the ignition works
When the thermostat calls for heat, the board sends voltage to the gas valve and the electrode for about 6–8 seconds. If no flame is sensed, it tries again. After three tries it locks out and the red light on the switch stays on.
Step-by-step: match what you see
STEP 1
Reset and watch the burner
Turn the switch off and on while someone watches at the outside door. Note whether you see spark, smell or hear gas, and whether it lights.
What happens?
Spark, but no gas
Low gas pressure (set 11 in. WC), low voltage (10.5 VDC minimum), a blocked burner or orifice, or a loose wire, dirty connector, bad ECO, board or gas solenoid.
Gas, but no spark
Loose high-voltage lead, electrode gap not 1/8 in. or out of the flame path, dirty or cracked electrode, or a bad board.
Spark and gas, still locks out
Pressure or voltage issues, a poor ground, electrode out of the flame or sparking to the burner screw, blocked burner or orifice, air shutter not about 1/4 open, or a gas solenoid opening only part way.
No spark and no gas
No 12V at the board, dirty board edge connector, or a bad thermal cut-off, on/off switch, board or thermostat.
STEP 2
Check for spiders and insects
Atwood and Dometic both warn that spiders and mud wasps nest in the burner tube. Signs: the burner sounds different, or the flame turns soft, lazy or yellow instead of hard blue. Clean the tube with a flexible wire brush.
STEP 3
Check the thermal cut-off
The thermal cut-off (93866) is a one-shot safety that trips at 190°F, usually because a blocked burner or flue overheated the area. If it’s open, clear the blockage and replace it. It doesn’t reset.
Still locking out with good gas, 12V and a clean burner?
Board or electrode
Atwood’s 93865 board and 93868 electrode come together in kit 91504. Check what fits your model; we can confirm by model number.
Gas solenoid valve
With 12V at the valve during a try and good pressure but no gas, the solenoid valve is suspect.
High-temperature lockout
If the heater shuts off because the water got too hot (the ECO opened), let the water cool, hold the switch off for at least 30 seconds, then turn it on. If it keeps happening, the thermostat may not be opening. See our thermostat and ECO guide.
Parts for this repair
Dometic/Atwood 91363 Ignition Control BoardView part →
Dometic 91365 Ignition Control BoardView part →
Dometic 91367 Ignition Control BoardView part →
Dometic/Atwood 93868 Electrode (Spark Probe)View part →
Dometic 91447 Front Mount ECO/Thermostat Kit (DSI)View part →
Dometic/Atwood 93866 Thermal Cut-Off KitView part →
Dometic/Atwood 91638 Main Burner, 6 Gallon (DSI)View part →Shop by category: Atwood parts, Dometic parts.
FAQ
Why is the red light on my Atwood water heater switch?
The heater tried to light three times and locked out. Turn it off and on; if it locks out again, check propane, 12V, the burner tube and the electrode.
What is the electrode gap on an Atwood water heater?
1/8 inch between the spark probe and ground, and the probe must sit in the flame path.
What fuse does an Atwood water heater use?
A 2 A mini ATO fuse. Atwood says never to install one larger than 3 A.
Can I reset the Atwood thermal cut-off?
No. The 93866 is one-shot. Clear the cause (usually a blocked burner or flue) and replace it.
Not sure which part fits? Contact us with your model and serial number from the data plate and we’ll confirm it before you order.
From the Atwood water heater service manual, Atwood/Dometic installation and operating manuals (MPD 93755/93756, Dometic 94035 and 3317866) and dometic.com.