RV Water Heater Fault Light On
The Short Answer: The red light on the interior LP switch is a DSI fault / lockout lamp, not a “heater on” lamp. It glows during the spark trial. It goes out when flame proves. It stays on after a few failed tries. One off/on cycle after the tank is full and the bottles are open. If it comes back, stop sparking. Hire an RV tech. Click-no-light is a different page.
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Search Intent & The Real Problem
You flipped the propane switch. A red LED lit. The shower is cold. Forums said “bad board,” “bad thermocouple,” and “reset it ten times.” Those are three jobs, and two of them dump unburned LP into a six-gallon bay.
Suburban Phase 3 and Atwood/Dometic DSI have no standing pilot. The board sparks, opens the solenoid, looks for flame. No proof = lockout, lamp stays on. Coach skins (Forest River, Keystone, Thor, Grand Design) are still Suburban or Atwood inside — Forest River, Thor, Grand Design. Click with no flame is Atwood clicking. Light-then-die is fires up then goes out. This page is the lamp that will not go out.
What other guides get wrong
They treat the red LED like a furnace “call for heat” that should stay on while it runs. On most Suburbans the fault light is supposed to go dark once the burner holds. They mix Atwood boards with Phase 3, so you buy a Dinosaur module with the wrong connector. They skip bypass, so you lock out a tank that has no water. And they still describe cracking a flare to “bleed air.”
Step-by-Step Troubleshooting
Step 1: Name the lamp — DSI fault vs electric vs ECO
| What you see | What it is | Next |
|---|---|---|
| Small red LED on the interior LP / gas rocker; glows ~6–15 s then dies, burner running | Normal trial | Leave it |
| Same LED stays on after the trial, no burner | DSI lockout | This page |
| Illuminated electric rocker, gas lamp dark | 120 V path — not this light | Atwood electric |
| No LED at all, no tick | 12 V, switch, fuse, board | Power path |
| Red ECO / black button on the tank jacket | High-limit, not the fault lamp | Fill, then Suburban RV reset |
- What to look for: Door badge: Suburban SW6DE / SW10DE / Phase 3 vs Atwood/Dometic G6, GC6, G10, WH-6. Interior gas switch, not the 120 V switch. Bypass in heat, tank full — steady stream at a hot faucet, no sputter. Electric switch off while you diagnose gas so you do not dry-fire the ~1400 W element.
- Required tools: Flashlight, the cabinet diagram, a hot faucet.
Atwood’s non-ignition lamp lives at the same interior switch. Same rule: lamp after the trial = lockout, not “it is heating.”
Step 2: Bottles, 12 volts, one trial — then stop
- What to look for: LP bottles actually open. Stove lights. Stove works and the heater lockouts = problem at the heater. Coach battery ~12.6 V rest; DSI boards act drunk under ~10.5 V. Converter in storage mode will lock a healthy board. Automatic changeover on reserve with both bottles empty looks like a $200 module.
- Required tools: LP gauge, voltmeter at a known-good 12 V point. No flare wrenches.
One switch cycle: off 15–30 seconds, on. Watch the exterior door. Tick, blue, lamp dies = proved. Tick, nothing, lamp stays = lockout. Do not give it three more “just in case” cycles. That is how bays fill with gas.
Step 3: Spark with the bottles off — before you buy a board
- What to look for: Bottles closed: you should still hear/see spark at the electrode during the trial. No spark: cracked ceramic, melted high-voltage lead, open thermal fuse, or a dead board — Suburban igniter, Dometic thermal fuse. Spark with bottles off, no flame with bottles on: solenoid, spider in the tube, or LP at the appliance. LP at a Suburban/Atwood burner is ~10–11 in. w.c. — confirm the rating plate; a manometer is a licensed/RV-tech job, not a union crack.
- Required tools: Eyes on the electrode with LP off. The interior switch. Never jumper the thermal cutoff “to test.”
A fuse that is open did its job. Find rollout, a blocked flue, or a storage cover over the exhaust before you clip in a new link.
Step 4: Why the lamp stayed on — the usual four
| Cause | What you see | Before another reset |
|---|---|---|
| Empty tank / bypass / winterize | Sputter at the tap, ECO open | Fill. Heat path. Then one cycle |
| Low LP or starving regulator | Stove fades when the furnace joins | Bottles, changeover, icing regulator |
| Dirty, cracked, or out-of-flame rod | Brief blue, then lockout | LP off; look, do not sand it live |
| Thermal fuse / ECO / low 12 V | Silent or one click, then lamp | Meter the fuse, voltage, one ECO on a full tank |
- What to look for: Soot on the door, wasp nest in the burner tube, bird screen packed, water dripping on the burner from a weeping P&T — shut LP; that is a leak, not a board. Standing-pilot antiques use a thermocouple at ~20–30 mV. Phase 3 and Atwood DSI do not. Wrong part, lamp still on.
- Required tools: Flashlight. LP off before you touch the rod. Finger on one cool ECO — SW6DE if the door says Suburban.
Broader gas death after the lamp is decoded: Suburban not working on gas, Atwood troubleshooting, Phase 3.
Step 5: Reset once — a lamp that returns is the end of DIY
- What to look for: Cause addressed (full tank, bottles open, 12 V healthy, flue clear). One off/on. Burner holds, lamp dark, no propane odor, no bang. Same red lamp on the next call is a solenoid, board, regulator, or a fuse you were about to jumper. Stop.
- Required tools: The switch. A watch. No paperclip across the thermal fuse. No tape on the ECO.
Do not “purge air” at a flare — do not purge it. Air after a bottle swap can stutter one trial. Yesterday’s heater that lockouts today is not air.
When DIY Ends: Calling a Licensed Pro
You may fill the tank, set bypass, confirm 12 V, watch one spark trial with LP off, and cycle the interior switch once. Stop at a propane smell, a repeating fault light, a thermal fuse you want to jumper, water in the burner box, and any solenoid or board swap. A mobile RV tech with a manometer and the correct Suburban vs Dometic harness beats a melted connector from the Amazon module that “looked close.” Same-day if it smells.
Frequently Asked Questions
Q: What does the fault light on an RV water heater mean? A: On Suburban and Atwood/Dometic DSI heaters the red LED on the interior LP switch is a lockout lamp. It lights during the spark trial and should go out when flame proves. If it stays on, ignition failed. It is not a “heater running” light.
Q: How do I reset an RV water heater fault light? A: Fill the tank, bypass off, bottles open. Turn the gas switch off 15–30 seconds, then on. Watch one trial. If the lamp stays, stop. Do not keep cycling. An ECO button is a different reset on a full tank with power off.
Q: Can I keep resetting the fault light until it lights? A: No. Each failed trial dumps unburned propane into the burner box. One reset after you fix the obvious cause. A lamp that returns is an RV-tech job — electrode, solenoid, fuse, LP pressure, or the board.