Truma Water Heater Flashing Light Codes
The Short Answer: A flashing Truma light is a lockout or a warning, not a “heater on” lamp. AquaGo: yellow knob LED plus a red LED on the box that speaks in short and long blinks. Combi: CP plus digits (E / W codes). Photograph the pattern. One off/on after water, 12 V, and LP are proven. If it returns, stop sparking. Hire an RV tech.
Licensed local technicians
Truma light flashing and the shower is cold?
Connect with a licensed 24/7 technician in your zip code right now.
Search Intent & The Real Problem
The interior knob is blinking. Or a red LED on the exterior door is Morse-coding. Showers are cold — or lukewarm after a decalcify you never finished. Forums paste Suburban DSI fault-lamp steps onto a Truma that has no 6-gallon tank ECO in the same place. AquaGo is on-demand LP. Combi is hydronic heat plus a small potable cylinder. Alde glycol boilers are a different Truma-owned machine — Alde not working, Alde problems. Generic no-heat without a flash count: AquaGo problems. Airstream bays: Airstream.
What other guides get wrong
They treat the yellow knob LED like a Suburban “on” lamp that should stay lit the whole shower. On AquaGo, a fast double flash after a pause means go read the red LED on the heater. They decode Combi E-codes with AquaGo short/long tables. They tell you to keep cycling after three failed flame trials. And they vinegar-flush a unit still open to the fresh tank because the light blinked during decalcify — that blink can be rinse complete, not a dead board.
Step-by-Step Troubleshooting
Step 1: Name the Truma — AquaGo vs Combi vs Alde
| What you have | Light language | This page |
|---|---|---|
| AquaGo Comfort / Comfort Plus / Compact, exterior door, on-demand | Yellow status on the interior knob; red LED on the heater (short/long) | Yes |
| CP plus screen with E / W digits (Combi eco / Combi heat) | Alphanumeric, not Morse | Yes, Combi folder |
| Alde 3010 / 3020 / 3030 panel, glycol | Different boiler | Alde |
| Suburban / Atwood tank, red rocker LED | DSI fault lamp | RV fault light |
| Girard / Furrion / Lippert tankless | E0–E4 style | Girard |
- What to look for: Door badge and the control you actually have. Photo of the yellow LED and the red LED (or the CP plus digits) before you cycle power.
- Required tools: Phone camera, flashlight, the sticker in that bay.
Step 2: AquaGo yellow vs red — count short and long
Interior knob: steady yellow is ready/on. Fast double-flash after a break is “there is a fault — read the heater.” Rapid flash during decalcify/rinse is a process, not a random lockout. Confirm in the AquaGo manual for that SKU.
Red LED on the box repeats an 8-beat pattern (short = 0, long = 1). Common field codes — your jacket table wins:
| Pattern (s = short, l = long) | Typical meaning | First move |
|---|---|---|
| s,s,s,s,s,s,s,l | Flame not detected (after three trials) | LP, 12 V, air at the flue — then stop |
| s,s,s,s,s,s,l,s | Exhaust / burner over-temp switch open | Do not fire it (CO / fire) |
| s,s,s,s,s,s,l,l | Exhaust pressure switch / blocked flue | Nest, snow, crushed hose — licensed if it repeats |
| s,s,s,s,s,l,s,s | Water over-temp switch | Flow, mixer, then licensed |
| Rapid yellow + “rinse” / E31-class | Decalcify rinse not finished | Finish the rinse per Truma, not a board |
- What to look for: Bottles open, other LP appliances light, coach battery ≥12.0 V at the unit, bypass/winterize normal, inlet strainer not packed with campground grit. Same water-power-gas order as the AquaGo hub.
- Required tools: Voltmeter, eyes on the filter, ears at the flue. Gas off if you only want to confirm the fan/spark once.
Step 3: One reset — then stop cycling
- What to look for: AquaGo: heater off 5–10 seconds, on. Combi: CP plus reset per that software, not ten power pulls. Flame-not-detected that returns on the next hot faucet is LP, an igniter, a blocked flue, or a board — not a second Morse lesson. Lights then dies is the same physics as RV fires up then goes out.
- Required tools: The interior control. No paperclip on over-temp switches.
Air after a bottle change delays ignition. Loosening flares is how bays fill with gas. Do not “bleed” the pigtail.
Step 4: Combi CP plus — voltage, empty cylinder, blocked air
Combi is not AquaGo. It heats glycol/air and a potable tank. Common CP plus language (confirm your handbook):
| Code (examples) | Meaning | DIY? |
|---|---|---|
| W 17 | Hot-water mode, empty cylinder | Cool down, fill, then on |
| W 18 / 9-flash yellow | Warm-air outlet or return blocked | Clear furniture, crush, winter covers |
| E 44 | Undervoltage (battery too low) | Charge / load shed — not a new Combi |
| E 43 | Overvoltage | Charging system — licensed 12 V |
| E 112 / E 202 / E 211 class | No flame / gas off / overheat protection | Bottles, then RV tech if it repeats |
- What to look for: 12 V at the Combi, 120 V only if that SKU uses it for a specific function, ducts actually open, water actually in the cylinder. Empty-tank electric heat on a Suburban is a different ECO — do not mash a Combi like an SW10DE.
- Required tools: Voltmeter, flashlight in the basement bay.
Step 5: Freeze, wet bay, and when the box is scrap
- What to look for: Battery disconnect pulled on a night below freezing with water still in AquaGo — freeze protection needs 12 V. Split exchanger, wet bay, ice: replacement, not a flash-code reset. Water at an exterior door on a tank coach is RV leaking outside, not a Truma LED. Decalcify that never finished will keep blinking until you rinse the volume Truma specifies.
- Required tools: Eyes. LP off. Do not epoxy a freeze-broken exchanger.
When DIY Ends: Calling a Licensed Pro
You may photograph the LED pattern, set bypass to normal, confirm 12 V and bottles, clean the AquaGo inlet strainer, and power-cycle once. Stop at propane odor, over-temp / blocked-flue codes that return, a wet bay after a freeze, and any jumper. AquaGo and Combi gas trains, over-temp switches, and heat exchangers are RV-tech / Truma-service territory. A mobile tech with the right Morse chart beats three Amazon “universal RV tankless” boards.
Frequently Asked Questions
Q: What does a flashing light on a Truma water heater mean? A: A fault or a process blink, not a run lamp. AquaGo uses a yellow knob LED plus a red short/long code on the heater. Combi uses CP plus E/W digits. Photograph it. One reset after water, 12 V, and LP are proven.
Q: How do I reset a flashing Truma AquaGo? A: Switch it off, wait several seconds, switch it on. If flame-not-detected or an over-temp code returns, stop. Repeated resets dump unburned LP. Hire an RV tech.
Q: Is a flashing Truma light the same as an RV fault light? A: No. Suburban and Atwood DSI rocker lamps are a different board. Truma Morse and CP plus codes are not a Phase 3 module. Wrong parts melt the harness.