A tankless water heater error code is the unit telling you where to look. Rinnai, Navien, Noritz and Rheem all show codes when something is wrong — ignition failure, flame loss, overheating, a blocked vent, a clogged filter. The code is the fastest route to the fix, and the tables below list the common ones, verified against manufacturer documentation.
Before anything else: write down the exact code, and the brand. A code that looks the same on two brands can mean different things, and a code that is one digit off is a different fault. If the unit is showing a code and there is no hot water, a gas smell, or water leaking, call (877) 418-1589 and read the code exactly as it appears.
What to check first, whatever the code
- Gas supply on. The gas valve fully open, other gas appliances working.
- Water supply on. The cold-water valve to the unit fully open.
- Power on. The unit plugged in, the breaker not tripped.
- Inlet filter clean. A clogged filter starves the unit of flow.
- Vent clear. Nothing blocking the intake or the exhaust.
Those five checks fix a surprising number of codes. If the code comes back after a single reset, stop resetting it — a code that returns is a fault, not a glitch.
Common error codes by brand
Every code below was verified against manufacturer documentation at the time this page was written. If a code cannot be verified, it is not listed here.
Rinnai
| Code | What it means |
|---|---|
| 10 | Blocked exhaust or air supply — venting is restricted |
| 11 | No ignition — the burner will not light |
| 12 | Flame failure — the flame lit, then went out |
| 13 | Abnormal combustion — the flame is not burning cleanly |
| 14 | Thermal fuse tripped — the unit overheated |
| 16 | Over-temperature — outgoing water is too hot, often scale |
| 25 | Venting or condensate blockage |
| 65 | Water flow control fault |
Navien
| Code | What it means |
|---|---|
| E003 | Ignition failure — the unit cannot light |
| E004 | False flame detection |
| E010 | Venting or air-pressure fault |
| E012 | Flame loss during operation |
| E016 | Heat exchanger overheating — often scale |
| E030 | Exhaust overheat |
| E110 | Exhaust or intake vent blockage |
| E438 | Clogged air intake filter |
| W003 | Maintenance reminder — a flush is due |
Noritz
| Code | What it means |
|---|---|
| 10 | Combustion abnormality |
| 11 | Ignition failure |
| 12 | Flame loss during operation |
| 14 | Thermal fuse failure |
| 16 | Abnormally high outlet water temperature — often scale |
| 20 | High-limit switch tripped — overheating |
| 29 | Condensate or neutralizer drain problem |
| 59 | Low gas input — combustion is starved of air or gas |
| 61 | Fan motor fault |
| 65 | Main water control servo fault |
| 66 | Bypass water control servo fault |
| 73 | Circuit board setting fault |
| 90 / 99 | Combustion abnormality |
Rheem
| Code | What it means |
|---|---|
| 1L | Lime and scale buildup in the heat exchanger |
| 05 | Air intake or vent exhaust blocked |
| 11 | No ignition — gas valve not open or no gas supply |
| 12 | No flame — gas service interrupted or low LP gas |
| 13 | Poor or improper combustion — flame rod fault |
| 29 | Neutralizer clogged |
| 61 / 99 | Blower motor fault |
| 65 | Water flow solenoid fault |
| P1 | Water flow too low to run the unit |
What affects the cost of an error-code visit
The code decides the cost, because the code decides the part. A clogged filter or a maintenance reminder is a small visit. A flame sensor or an igniter is a part replacement. A control board or a heat exchanger is the expensive end. The provider's first job is to confirm what the code actually means on your unit, because a code is a clue, not a diagnosis — two different faults can show the same code.
Questions people ask
What does my tankless water heater error code mean?
It depends on the brand and the code. Rinnai 11 means no ignition; Navien E003 means the same thing on a Navien. The tables on this page list the common codes for Rinnai, Navien, Noritz and Rheem, verified against manufacturer documentation.
Can I reset a tankless error code myself?
You can try once — turn the unit off, wait a minute, turn it back on. If the code comes back, stop resetting it. A code that returns is the unit telling you something is wrong, and repeated resets do not fix the cause.
My unit shows a code that is not on this page. What now?
Call (877) 418-1589 and read the code exactly as it appears, with the brand. Some codes are rare, some are model-specific, and some mean a board or sensor fault that only a provider can confirm.
Is an error code an emergency?
It is urgent when there is no hot water, a gas smell, or water leaking. A maintenance reminder like Navien's W003 is not an emergency — it is the unit asking for a flush. Everything else sits in between: call, describe the code, and the provider will say how soon it needs a visit.
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