Water Heater Error Codes: Every Brand, Every Code Explained

Every water heater watches the same short list of things — water flowing, a burner lighting, flame staying lit, exhaust leaving, temperatures staying inside their limits — but each brand reports trouble in its own language: a two-digit display code on a tankless unit, a counted flash pattern on a tank's gas control, a three-digit code on an electronic tank control, or an alarm on a smart control. This page is the index: how the languages divide, the ignition and flame faults every brand shares, and the six full brand lists we publish — Rheem, AO Smith, Bradford White, Navien, Rinnai and Bosch — each built from that maker's own documentation.

How water heater codes work: three reporting languages

The first language is the display code, spoken by tankless heaters and electronic tank models: a number or letter pair on a screen or remote — Rheem's 11 and 12, Navien's E003, Rinnai's 11, AO Smith tankless 111, Bosch's EA. The control lights (or refuses to light) a burner in a strict sequence — fan, airflow proof, ignition spark, flame proof, sustained burn — and the code names the step that failed, which is why display codes cluster into ignition, flame, airflow/venting, flow and temperature families. The second language is the counted flash: most gas tank heaters have no display at all, and their gas control speaks through one status LED, blinking in patterns whose legend is printed on the control itself — Bradford White's controls are the textbook example, and Rheem and AO Smith tank controls use the same idea. The third language is the smart alarm: connected controls on newer tank models that show a code on a small display, push an alert to an app, and sometimes beep — the same fault, delivered three ways at once.

What unites the languages is the sequence underneath them. Every gas water heater, tank or tankless, must prove the same chain before it may heat: a call for heat, air moving, ignition attempted, flame proven by a sensor, exhaust leaving, and water temperature rising but not overshooting. A code is a named break in that chain, and the family it belongs to tells you which link broke — which is more useful than the digits, because the digits are not portable. Eleven means ignition failure on a Rheem tankless and on a Rinnai, something else again in another brand's table, and nothing at all on a Bradford White, which has no numbers to give. Read the family first, the brand's table second, and never a number in a stranger's chart.

Tank vs tankless: why the code lists look so different

Tankless heaters carry the longer lists, and the reason is mechanical: a tankless unit must modulate a powerful burner second by second against flowing water, so it supervises far more of its own behaviour — flow rate, inlet and outlet temperatures at several points, fan speed and airflow, condensate drainage on condensing models, even the barometric pressure on Bosch's Greentherm. Its codes are correspondingly granular, splitting one physical event — the exhaust running hot — into sensor, derate and shutdown reports. A tank heater's burner is a simpler, slower device heating a stored volume, and its control supervises a shorter chain: pilot or electronic ignition, flame proof, temperature sensing, and the gas control's own health. Its reports are correspondingly fewer and blunter — on flash-pattern controls, a handful of patterns cover the whole machine.

The practical consequence is that the two platforms fail differently on paper. A tankless code usually names a component or a step (this sensor, that airflow proof), while a tank code usually names a condition (ignition failed, control fault, temperature fault) and leaves the component hunt to the technician. Maintenance codes split the same way: descaling and inlet-filter reports exist only where a heat exchanger and a fine water path exist — the tankless side — while a tank's closest equivalents are sediment and anode stories that no control can see and therefore no code reports. When you open a brand list below, open the platform section for your machine: the same brand sells both, and its tankless table will confidently mislead a tank owner.

Reading a code before you reset anything

Freeze the evidence first. Photograph the display, or video the status light through one full pattern cycle — counted flashes are a code, and a pattern remembered approximately is a different code. Write down what the house was doing: a long shower ending, the first draw of a cold morning, a power cut just before, several taps open at once. Tankless codes in particular are event reports — a flame code at maximum draw with every tap open and an ignition code on the first small draw of the day are different stories wearing related labels. Note, too, whether hot water exists at all: no hot water anywhere, water that starts hot and runs cold, and hot water with a code showing are three different branches, and the code's family plus that branch is most of the diagnosis.

Then do the external checks the code's family points to, and only then reset — once, the way the brand documents, while you run one hot tap and watch the sequence. A code that returns at the same stage (fan starts but no ignition click; ignition clicks but no flame; flame lights then dies) has told you its stage, which is the information a technician will ask for first. A code that never returns was an event — a gust at the vent termination, a momentary gas-pressure sag — and noting the date is the whole correct response. What resetting cannot do is clear a standing fault: every brand's control re-tests its sensors on the next call for heat, and a fault that is still true re-reports, on some controls into a lockout that then needs the documented recovery. Reset last, not first.

Rheem water heater error codes

Rheem reports in two dialects split by platform. Its tankless heaters use two-digit display codes in which the low teens are the combustion heartland — 11 is ignition failure, 12 is flame failure — with neighbouring numbers for airflow, exhaust and temperature faults, read on the unit's display or its remote. Its tank heaters mostly speak through the gas control's status light, in counted flash patterns whose legend is printed on the control, backed on electronic and smart models by display codes and app alerts. Rheem also builds under related badges, but the code table to trust is always the one in your model's own manual — Rheem's platforms have never shared one list.

Full list: Rheem Water Heater Error Codes List — every verified Rheem code with causes and first fixes.

AO Smith water heater error codes

AO Smith's tankless line uses three-digit display codes — 111 is its ignition-failure code — in a system it shares with its tankless platform's documentation, organised by the step of the firing sequence that failed. Its tank heaters divide by control generation: the large installed base of gas tanks reports through the gas control's status-light flash patterns (legend on the control), while AO Smith's electronic and smart tank controls show codes on a display and raise app alerts, including leak-detection alarms on equipped models. Name the control, not just the brand, before opening a table: an AO Smith flash pattern and an AO Smith three-digit code are different languages.

Full list: AO Smith Water Heater Error Codes List — every verified AO Smith code with causes and first fixes.

Bradford White water heater error codes

Bradford White is the flash-pattern brand: its residential gas tank heaters report through the status light on the gas control, in counted blinks and steady or dark states, with the decoding legend printed on the control itself — there is no numeric code list to look up, and any site offering one for a Bradford White tank is borrowing another brand's table. The patterns divide into normal-operation indications, pilot and ignition faults, temperature-sensing faults and gas-control faults, and the control's label is the authority for your exact model. Its tankless Infiniti line, by contrast, uses display codes — the platform rule again: Bradford White tank, count flashes; Bradford White tankless, read the screen.

Full list: Bradford White Water Heater Error Codes List — every verified Bradford White code with causes and first fixes.

Navien water heater error codes

Navien reports with E-prefixed three-digit codes on its tankless units — E003 is ignition failure, E110 is an air-pressure / exhaust abnormality — shown on the front display and, on connected models, pushed through its app with the same code attached. Navien's system is unusually willing to name subsystems: separate codes cover the flow sensor, the various temperature sensors, the fan, the condensate path and the recirculation system on equipped models, so a Navien code often reads like a parts diagram entry. That precision cuts both ways: the codes are model-scoped within Navien's own generations (NPE, NPN and NCB combi-boilers overlap heavily but not completely), so quote code and model together.

Full list: Navien Water Heater Error Codes List — every verified Navien code with causes and first fixes.

Rinnai water heater error codes

Rinnai's tankless heaters use two-digit display codes with the combustion sequence at the top of the table: 10 is an air supply or exhaust blockage, 11 is no ignition, 12 is flame failure — the three codes that account for most Rinnai service calls, and a tidy summary of what a tankless burner must prove (air, spark, flame). Codes are read on the unit or its remote controller, and Rinnai's documentation distinguishes codes that lock the unit out from warnings it can run through. Rinnai numbers are not portable even inside the wider industry: its 11 and Rheem's 11 agree on ignition by coincidence of design, not by standard, and its other numbers diverge quickly.

Full list: Rinnai Water Heater Error Codes List — every verified Rinnai code with causes and first fixes.

Bosch water heater error codes

Bosch tankless heaters use letter-plus-digit display codes sorted into families — A for temperature sensors, C for combustion air, venting, fan and water valves, E for over-temperature cut-offs, flame supervision and control faults, F for control, configuration and gas-path faults — with EA (ignition failure) and EC (flame lost in operation) the shared ground between Bosch's two generations. The generations are the catch: the current Greentherm 9000 (T9900/T9800) and the older Therm / C models reuse letters with different meanings (A2 is an aquastat sensor on a Greentherm, the flue gas limiter on a Therm), so Bosch codes are always read scoped to the generation, exactly as this site's Bosch list presents them.

Full list: Bosch Water Heater Error Codes List — every verified Bosch code with causes and first fixes.

The codes every brand shares: ignition and flame

DIY check or licensed job? The line the codes themselves draw

The owner-level half of every water heater code is the world outside the cabinet: power present and the unit's switch on, the gas cock fully open, intake and exhaust terminations clear of snow, nests, mulch and debris, the tankless inlet water filter rinsed, the condensate trap and drain unfrozen and unblocked on condensing models, breakers untripped, and — on a tank — a look at the base for leaks and at the T&P valve's discharge pipe for drips. Those checks genuinely cure the environmental share of every brand's codes: blocked terminations behind airflow codes, clogged inlet screens behind flow and temperature codes, a drained condensate trap behind shutdowns after dry spells. They require no tools beyond a torch and no opening of anything sealed.

Everything inside the cabinet is the licensed half, and the boundary is not a courtesy — it is where gas, combustion and pressure live. Igniters, flame sensors, gas valves, burners, heat exchangers, venting runs, control boards and the T&P valve itself are professional territory in every brand's own manual, several of which print exactly that restriction beside their code tables. The codes help you respect the line: a code whose family is airflow deserves its termination check from you and its internal fan and venting inspection from a technician; a code whose family is the gas valve (Bosch's FA is the bluntest example) deserves a shutoff and a phone call from you and nothing more. When in doubt, ask what the check touches: if the honest answer is gas, flame, exhaust or pressurised hot water, it is not a DIY check.

The reset-last rule, and the lockout behind it

Every water heater control treats a reset as 'try again', and several treat repeated failure as a reason to stop asking. Ignition lockout is the standard example across brands: after a set number of failed lighting attempts, the control stops cycling — protecting the burner from flooding with unburned gas and the house from a heater that retries forever — and requires the documented recovery, which ranges from a power cycle and a wait, to a specific button hold, to a technician's visit on controls that count lockouts as evidence. An owner who resets ten times in ten minutes has not done ten tests; they have defeated a safety counter and destroyed the fault history that would have shown the pattern. The correct rhythm is the one this site repeats on every brand page: record, check externally, reset once, observe the stage of failure, and let a returning code stand as the technician's starting evidence.

One reset deserves its own warning, because it is the one owners reach for first: the breaker. Cycling power clears volatile memory on many controls, which makes it feel like a fix — the code is gone, the heater runs. But it also erases, on some models, the stored fault history and the pattern evidence, while changing nothing about the scaled heat exchanger, the failing sensor or the marginal gas pressure that produced the code. Bosch's manuals state the honest version plainly — the reset removes the code from the display — and pair it in the same table with the cause checks. Use the brand's documented reset (a button hold on a Greentherm, the reset button on a Therm, the control's own procedure on a tank), use it after the checks, and count a code that survives two honest reset-and-observe cycles as diagnosed: it is a standing fault with a name, and its repair is the next step.

How to diagnose any water heater code

Work the problem in this order — and stop wherever gas piping, the burner compartment, venting or the temperature-and-pressure relief valve begins, because those belong to a licensed technician: (1) record the report exactly — a counted LED flash pattern, a numeric display code, or a smart-control alarm are three different languages, and a photograph or video beats a memory of any of them; (2) establish the water story: is there no hot water at all, water that runs cold mid-draw, or water but with a code — tankless codes split into ignition, flame, airflow/venting, flow and temperature families, and tank codes into ignition, sensor and control families, and the family picks the checks; (3) run the owner-level external checks for that family first: power and the unit's switch, the gas cock fully open, intake and exhaust terminations clear of snow, nests and debris, the inlet water filter or screen rinsed (tankless), the condensate trap and drain not blocked or frozen (condensing models), and on tank models the status light read before anything is reset; (4) reset once, the way the brand documents, and run hot water at one tap while you watch — a code that returns at the same stage (fan start, ignition click, flame light, sustained burn) is an active fault naming its stage, not a glitch; (5) everything past that line — flame sensors and igniters inside the burner, gas valves, heat exchangers, control boards — is professional work with the gas supply and a meter involved. Two standing cautions: never plug or cap a dripping T&P relief valve (it is reporting pressure or temperature, and it is the tank's last safety device), and treat any gas smell as an emergency — leave and call the gas utility. Scalding is the quiet hazard in every reset: a control fault that lets outlet temperature drift high is a reason to stop using the water on skin until the code is resolved.

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