RV Water Heater Fires Up Then Goes Out

The Short Answer: An RV water heater that lights, then dies, is proving flame and losing it: low LP, a dirty or cracked sense electrode, a thermal fuse or ECO, a starving regulator, or a DSI board in lockout. It is not “air in the line” you bleed at a flare. Watch one trial. If you smell propane, shut the bottles. Click-no-light is a different page. Electric still working means the tank can hold water.

Search Intent & The Real Problem

You hear the tick, see a blue puff, then it goes dark. Or a standing-pilot model lights, you release the button, and it dies. People keep hitting the interior switch. That dumps unburned LP into a small bay. Suburban Phase 3 and Atwood/Dometic DSI have no standing pilot: spark, solenoid, flame sense on the same rod. Light-then-die is sense, fuel, or a cutoff. Click with no flame is Atwood clicking or Suburban igniter. Broader Suburban gas death: not working on gas. Residential stay-lit: won’t stay lit.

What other guides get wrong

They lead with “purge the gas line” on a heater that fired yesterday. They mix standing-pilot thermocouples with DSI flame rods, so you buy a 20–30 mV thermocouple for a board that does not use one. They tell you to jumper the Atwood thermal cutoff “just to test.” And they diagnose gas from the electric switch, so you replace a 1400 W element because the flame will not hold.

Step-by-Step Troubleshooting

Step 1: Name the ignition, and prove it is light-then-die

• What to look for: Door badge: Suburban Phase 3 vs Atwood/Dometic vs an old piezo standing-pilot. Bypass valves in normal, tank full, water at a hot faucet without sputtering. Electric switch off while you diagnose gas so you do not dry-fire the element.
• Required tools: Flashlight, the cabinet diagram, a hot faucet.

Coach-brand skins (Keystone, Forest River, Thor) are still Suburban or Atwood inside — Forest River, Thor.

Step 2: LP supply that looks like a bad board

• What to look for: Bottles actually open. Automatic changeover on reserve with both empty. Regulator icing after a shower and a furnace and a fridge all drew at once — the heater lights, then starves, then lockouts. Two 20 lb tanks and a cheap regulator that will not hold ~10–11 in. w.c. at the appliance (confirm the rating plate; manometer is licensed). Other LP appliances dying in the same minute is the tank or regulator, not the DSI board.
• Required tools: LP gauge, eyes on both bottles. No flare wrenches.

Do not crack a fitting to “see if you have gas.” A licensed RV tech hangs a manometer.

Step 3: One spark trial with the bottles off, then on

• What to look for: Bottles off: you should still hear/see spark at the electrode. No spark: cracked ceramic, melted high-voltage lead, or a dead board — Suburban igniter. Spark with bottles off, flame with bottles on that dies in 3–8 seconds: the rod is not sensing, the flame is lifting off the rod, or a cutoff is opening. Soot, a spider web, or a warped burner tube will light and blow out. Do not keep cycling into lockout.
• Required tools: Eyes on the electrode with LP off. The interior switch.

Atwood/Dometic: a one-shot thermal fuse in the 12 V path will let it try, then go silent. Never jumper it. Find the rollout or blocked flue first.

Step 4: ECO, empty tank, and lockout reset — once

• What to look for: Winterize or bypass left on: tank empty, gas tries, ECO or high-limit opens, flame dies. Fill it. Electric ECO is the red button — one press on a full tank, power off first — Suburban RV reset, Atwood electric. DSI lockout: cycle the interior gas switch 15–30 seconds after a confirmed full tank and a confirmed spark. If it lights and dies again, stop. Phase 3 board logic: Phase 3.
• Required tools: Full tank, then one reset. Finger, not tape.

Standing-pilot thermocouple should make ~20–30 mV with a stable pilot. That measurement is a tech step, not a reason to hold the button in forever.

Step 5: Sense rod, flue, and a board that is actually dead

• What to look for: Electrode cracked, gap huge, rod not in the flame, wire melted to the jacket. Flue or bird screen packed — rollout, thermal fuse, light then out. Water dripping into the burner from a leaking P&T or a drain — shut LP; that is a leak article, not an igniter. Board that clicks a relay and never holds the solenoid after a clean rod and good LP is replacement, with the correct Suburban vs Dometic harness.
• Required tools: LP off before you touch the rod. The matching part number.

Do not sand a live electrode with the gas on. Do not convert “air in the line” into a loosened flare.

When DIY Ends: Calling a Licensed Pro

You may confirm bottles, bypass, a full tank, and watch one spark trial with LP off. Stop at a propane smell, a repeating lockout, a thermal fuse you are tempted to jumper, gas-valve work, and any water in the burner box. A licensed RV tech with a manometer and the right board beats a melted harness from the wrong Amazon module. Same-day if it smells or the bay is soggy with unburned LP.

Frequently Asked Questions

Q: Why does my RV water heater fire up and then go out? A: Low LP, a dirty or cracked flame-sense electrode, an ECO or thermal fuse, or a DSI lockout. Watch one trial. If it dies again, hire an RV tech. Do not keep cycling the switch.

Q: Is it the thermocouple if my RV water heater lights then dies? A: Only on standing-pilot models. Suburban Phase 3 and Atwood/Dometic DSI use a spark electrode and a board, not a 20–30 mV thermocouple. Wrong part, still no heat.

Q: Can air in the propane line cause the RV water heater to light then go out? A: After a bottle swap it can stutter. That is still not a DIY flare purge. If it ran yesterday, look at LP level, the regulator, and flame sense, then hire an RV tech.