AO Smith Tank Display Codes (E01, E02, E03, E04, ECC, 001, 022, 031): Meaning & Fixes

AO Smith's tank models with real displays — the Electronic Thermostat (ET) electric line and the smart Control Assembly models — report faults as E-codes beside a flashing LED, or as three-digit numbers on the smart display. This system article treats each verified display code in turn: E01, E02, E03, E04 and ECC from the ET and Voltex tables, then 001, 022 and 031 from the smart Control Assembly chart. It closes with three codes, B2-70, BE-1 and BD-0, that circulate in search results but could not be verified in any AO Smith document — named there, without meanings, on purpose.

Which display is talking: ET flashes versus the smart Control Assembly

Two tank platforms put codes in front of the owner, and they must be separated before any code is read. The Electronic Thermostat platform — AO Smith's ProLine electric models with the ET control — pairs each E-code with a counted red flash pattern: E01 is one flash, E02 two, E03 three, E04 four, E05 five, while a green flash means normal operation and no light means no power to the board. The code and the count are the same message in two forms, so if they ever disagree, believe the pairing is telling you the display was misread. The smart Control Assembly platform — fitted to smart tank electrics and the Voltex MAX hybrids — shows three-digit numbers on a digital display, adds a flashing alert indicator and beeper for serious faults, and runs a much longer chart: dry-fire 001, thermistor faults 003/004, processor fault 006, element circuits 021/022, a leak at 031, anode and valve reports in the 040s, and the heat-pump family in the 080s. The overlap is the trap: both platforms have a dry-fire report and an over-temperature report, but the ET calls them E01 and E02 while the smart control calls the dry-fire 001 and handles over-temperature through its ECO hardware rather than a numbered code. E-codes in this article are therefore always labelled ET or Voltex; the three-digit codes are always the smart chart. Find your platform on the rating plate and the control itself before you look anything up — the thirty seconds that takes is the whole difference between this article helping and misleading you.

Code E01 (ET): dry-fire

On the Electronic Thermostat platform, E01 — one red flash — means dry-fire: electrical power was applied while the tank was not completely full of water. An element energised in air instead of water overheats in seconds, because the element's heat has nowhere to go; the ET watches for exactly this signature at fill time and reports it rather than letting the element cook. AO Smith's corrective action is a refill done properly: turn off electrical power at the breaker, add water — meaning open the supply, and run a hot faucet until water flows steadily with no air bursts, which is the only proof the tank is genuinely full — then turn the power back on. The code exists because the most dangerous moment in an electric tank's life is the hour after installation or draining, when enthusiasm restores power before plumbing is finished; plumbers call the result a dry-fired element, and it is the commonest self-inflicted wound in water heating. Two follow-through points. If the code clears and the heater heats normally, the protection caught the event in time and no harm is expected. If it clears but recovery is afterwards slow or one element seems dead, the element was likely damaged in the interval before the control intervened — an element circuit test belongs to the E04/E05 family below. And if E01 appears on a heater nobody has drained, suspect the fill itself: a closed supply valve, a failed fill after a long vacancy, or a major hot-side leak emptying the tank faster than it fills. Dry-fire is a report about water level at power-up; on an untouched heater, the water went somewhere.

Code E02 (ET): water temperature exceeded the high limit

E02 on the ET platform — two red flashes — means the water temperature exceeded the high limit: the tank overheated and the safety side of the control intervened. This is the display-platform cousin of the gas control's 4-flash event and deserves the same respect, because the limit it names exists to prevent scalding water and, beyond that, a pressurised tank heated past its design. AO Smith's procedure is the classic high-limit reset, performed in the manual's exact order: turn off electrical power at the breaker; press the reset button; turn the power back on; and if the error returns, call a service technician. What that procedure hides is the question a good technician asks before pressing anything: why did the tank overheat? The reset restores a tripped safety; it does not repair the failed regulation that tripped it — a thermostat or ET that has lost control of an element, an element grounded and heating uncontrolled, or a control reading temperature wrongly. A one-time E02 after a power anomaly or a thermostat set recklessly high (the manuals warn repeatedly that settings above 120 degrees raise scald risk sharply, and that higher water can also stack in layers far hotter than the setting) may genuinely be an event. An E02 that returns within days is a condition, and the heater should stay off pending service — each return trip is the safety catching the same runaway again. Note, for cross-platform honesty, that E02 on AO Smith's electric tankless models is a different document's code for a hardware over-temperature determination; the fix philosophy is identical even though the platform is not: power off, and treat recurrence as a service call, not a reset routine.

Code E03 (ET): upper thermistor sensor failure

E03 on the ET platform — three red flashes — reports an upper thermistor sensor failure, and AO Smith adds the construction detail that decides the repair: the upper thermistor sensor is part of the Electronic Thermostat itself. The thermistor is the control's thermometer, the sensor whose resistance the ET reads to know the tank's upper temperature and to run the upper element. When it fails, the control is blind at exactly the point where regulation and the high limit are judged, so the heater faults rather than heat on a guess. The manual's corrective action contains no cleaning, reseating or adjustment step, because the sensor is not a separate field part on this platform: turn off power at the breaker, replace the Electronic Thermostat, turn the power back on. That is technician work for most owners — it involves the control's wiring at the top of a 240-volt appliance — though the diagnosis itself is mercifully binary: the code names the failed assembly, and replacing it either clears the fault or exposes a wiring problem the new control will report again. The smart platform's parallel is worth knowing if you are comparing models: its thermistor codes 003 and 004 name upper and lower sensors that are separate, tank-mounted parts, replaceable without replacing the control, and the smart control keeps heating on the surviving element in Limp Mode while it waits. The ET platform offers no limp — with its thermometer dead, everything stops, which is the honest behaviour. Do not confuse this E03 with the electric tankless E03, low water level; the shared string is the strongest argument in this whole article for naming your platform before your code.

Code E04 (ET): upper element circuit failure

E04 — four red flashes — means the upper element circuit has failed, and AO Smith's chart adds the reassurance that defines the ET platform's redundancy: the lower element is still operable. A two-element tank heats in sequence, upper first; with the upper circuit dead the heater falls back to its lower element alone, which in practice means hot water that exists but runs out faster and recovers slowly — the symptom owners describe as 'the heater shrank'. The manual's diagnosis is a proper electrical workup, done with the power off at the breaker. Check the element circuits for resistance of 5 to 25 ohms, replacing any element outside that range; check the wires at the elements and at the Electronic Thermostat for damage; and if the four-flash condition continues after the element and wiring prove good, replace the Electronic Thermostat itself, because the fault then lives in the control's switching of that circuit. That sequence — element, wiring, control — is the order to insist on, because elements are consumables that genuinely fail open or shorted to their sheath, while controls are condemned far more often than they fail. Sediment is the silent party to most element deaths: a tank never flushed buries its lower element region in scale and cooks elements early, so an E04 visit that does not include a drain-and-flush conversation is an incomplete one. The owner-level triage is symptom recognition and timing — E04 with lukewarm-but-present hot water is a planned repair, not an emergency — while everything involving element resistance and terminal wiring is power-off, qualified-person work on a 240-volt circuit.

Code ECC: the Voltex compressor report, in a display article

ECC appears in this article because owners meet it on a display and search for it here, but its scope must be stated first: ECC belongs to the older Voltex hybrid platform, defined in AO Smith's hybrid manual as the heat pump compressor not functioning, and displayed on that platform's word-based table as HEAT PUMP CONNECT FAULT. It is included, fully treated, in the hybrid system article on this site; the summary here exists so this article's readers are not sent away empty. The substance in brief: the heat pump's compressor is not running when the control expects it to; the resistance elements take over the heating, so the visible symptom is usually economic — an electric bill that has lost the heat pump's efficiency — rather than a cold shower; the manual's corrective action is to contact a qualified person to service the heat pump, with no owner repair step offered; and the smart platform's translation of the identical verdict is code 084. The neighbouring Voltex codes ECC owners should also report if seen are EUC and ELC (upper and lower element not functioning), ECF (compressor starting and stopping frequently — the short-cycling warning that can precede a compressor failure), and the sensor families E10 through E51. A hybrid that shows ECC alongside any of those is handing the technician a pattern, and patterns are what separate a compressor replacement from a control or sensor repair. If your display shows ECC, the hybrid article is your next page; if it shows E-codes E01 to E05 with flash counts, you are on the ET platform and the earlier sections of this article are yours.

Code 001 (smart Control Assembly): dry-fire

On the smart Control Assembly chart, 001 is dry-fire — electrical power on with the tank not completely full of water — announced with the alert indicator flashing, the red LED flashing and the beeper sounding, the platform's full alarm treatment for a fault that can destroy an element in under a minute. It is the smart descendant of the ET's E01, and AO Smith's corrective action follows the same logic in the smart manual's fuller words: turn off electrical power at the breaker; add water, opening a hot water faucet to bleed all air until water flows without air bursts; then turn the power back on, with a cross-reference to the manual's safety section that owners should actually read, because it covers the scald table — water at 140 degrees burns in seconds — that governs every refill and test that follows. The smart platform adds context the ET never had: 001 sits at the head of a chart where the control separately reports a processor fault (006), low supply voltage (009) and a water leak (031), so a 001 on a newly installed smart heater has differential diagnoses a basic tank lacks — an installation energised before filling, certainly, but also a leak emptying the tank (which 031 may confirm) or a fill defeated by a shut-off valve fault (046 on models fitted with the automatic valve). Practical handling mirrors E01: clear it by a proven full refill, watch the first heat cycle, and treat any immediate return as information — either the tank is still not full (find out why, with the power off) or the control's level judgement itself needs service. An element that survived a brief dry-fire may still have a shortened life; if an element circuit code (021/022) follows within weeks, tell the technician the 001 story, because it is probably chapter one of the same failure.

Code 022 (smart Control Assembly): lower element circuit failure

Code 022 on the smart chart means the lower element circuit has failed — and its sibling 021 names the upper circuit — each announced with the alert indicator and red LED flashing. AO Smith's chart gives the surviving context owners most want to know: with 022 showing, the upper element is still operable, and the control formalises that fallback as Limp Mode 2, satisfying calls for heat with the upper element until the failure is corrected. The lived symptom is a heater that works but underwhelms — recovery stretches, back-to-back showers run tepid — because the tank has lost the element that does most of its routine heating. The corrective procedure is the platform's standard electrical sequence, power off at the breaker throughout: check the element circuits for resistance of 5 to 25 ohms and replace any element outside that range; check the wires at the elements, the thermostat and the Control Assembly board for damage; restore power; and if the error persists, contact a qualified person — the chart's polite phrase for 'the fault is now in the control or its switching, and guessing further is not a plan'. AO Smith stands behind this code's importance with its own troubleshooting video for the Voltex MAX line titled by the code number, which is a useful pre-visit watch for owners who want to see the control's behaviour. The root-cause conversation matters as much as the swap: lower elements die early in sediment, and a tank that has never been flushed will eat its replacement on the same schedule, so the visit that replaces the element should also drain and flush the tank and check the anode — the unglamorous work that turns a code from an annual event into a one-time story.

Code 031 (smart Control Assembly): water leak detected

Code 031 on the smart platform means a water leak — and it must be introduced with its collision, because 031 is also the tankless platform's dipswitch code, and the two could not be more different in urgency. On a smart tank or Voltex MAX, 031 arrives with the full alarm set — alert indicator, flashing red LED and beeper — because the control's leak detection has found water where water should not be. AO Smith's corrective action is a leak hunt with the power already treated as guilty until proven innocent: turn off electrical power at the breaker and check all electrical connections and wiring for damage; check for plumbing leaks and correct them; if the tank itself is leaking, replace the unit; then restore power. Read the second and third steps together, because they are the whole decision tree of water heating: leaks divide into plumbing leaks — unions, the T&P valve weeping under high pressure or thermal expansion, the drain valve, the condensate line on a hybrid — which are repairable, and tank leaks, where water weeps from the vessel itself through a corroded seam or fitting boss, which are not. No sealant, patch or additive fixes a leaking tank; the vessel has reached end of life, and every day of delay is water damage accumulating in exchange for nothing. The smart platform exists partly for this moment — detection while the leak is a drip with an alarm, instead of a ceiling stain downstairs. Owner actions are immediate and simple: power off, water supply to the heater off if the leak is active, photographs of where the water appears for the technician or the warranty claim, and the model and serial number from the rating plate. Then the call — and on a tank leak, the conversation to prepare for is replacement, ideally while the warranty file is still warm.

Codes we could not verify: B2-70, BE-1 and BD-0, named without meanings

This guide closes with an act of deliberate omission, and it is worth explaining why these three strings get a section but no definitions. B2-70, BE-1 and BD-0 circulate in web search results and on third-party troubleshooting pages as AO Smith display codes, and readers arrive here looking for them. For this site, every code meaning must be verified against two manufacturer sources — AO Smith's own manuals, support pages and official documents. These three failed that test completely. No AO Smith manual checked for this article — not the ET diagnostic chart, not the smart Control Assembly chart in the current hybrid guide, not the older Voltex table, not the electric tankless chart, not any gas control chart — contains B2-70, BE-1 or BD-0, and no AO Smith support page defines them. The only treatments that exist are on aggregator and AI-generated advice pages, which contradict each other and cite no manufacturer document; the meanings offered there may be invented, borrowed from another brand's platform, or garbled from a model-specific display this research could not reach. Publishing any of them here would launder a guess into a fact, and a wrong meaning on a gas or high-voltage appliance is worse than no meaning at all. The useful advice is procedural: if your heater genuinely displays one of these strings, photograph the display together with the model and serial number from the rating plate, and put both in front of AO Smith Technical Assistance or a dealer who can query the model-specific documentation — the code may belong to a regional, commercial or discontinued control whose literature is not public. And if the string came from a search result rather than from your own display, treat that result the way this site treats it: unverified until a manufacturer document says otherwise.

Key takeaways

• Identify the platform first: E-codes with counted red flashes are the Electronic Thermostat chart; three-digit numbers with an alert indicator are the smart Control Assembly chart.
• E01 and 001 are the same event — dry-fire — in two dialects; the fix is a proven full tank (hot faucet running air-free) before power is restored, never power first.
• E02's reset is a procedure, not a cure: power off, press the reset, restore — and a return of E02 means the overheating cause needs a technician, urgently.
• On ET models the upper thermistor is part of the thermostat itself, so E03 ends at ET replacement; on smart models the thermistors are separate parts (003/004).
• 031 means dipswitches on a tankless and a water leak on a smart tank — the most dangerous code collision in the AO Smith range; platform first, always.
• B2-70, BE-1 and BD-0 have no verified AO Smith meaning; photograph the display and the rating plate and go to AO Smith Technical Assistance rather than trusting aggregator pages.

Resetting the AO Smith water heater

AO Smith documents a different reset for each platform, and none of them is 'keep cycling it until it behaves'. Tankless units reset by power: turn the unit off, restore power, and let it retry — the fault returns at once if its cause (gas pressure, venting, a soot-covered rod) is still present, which is the diagnosis, not a second fault. Smart Control Assembly units power-cycle at the breaker per the chart's 'Power Cycling the Unit' procedure; element and sensor codes persist until the part is fixed, while the ECO behind an over-temperature event is reset at the upper access panel with power off. Tank electric models with conventional or ET thermostats use the red high-limit reset button behind the upper access panel: power off at the breaker, press until it clicks, restore power — a button that trips again has a cause, usually a failed thermostat or grounded element. The knob-type gas control resets by relighting the pilot per the label, with its built-in ten-minute wait between attempts; the powered Intelli-Vent control clears most codes by turning power off for 10-20 seconds, and its flammable-vapor lockout needs the documented two-button Vacation-LED sequence. One reset after a fixed cause is service; repeated resets are how protected heaters get damaged.

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Facts on this page were checked against manufacturer documentation: www.manualshelf.com · manuals.plus · www.takagi.com · www.takagi.com · www.Takagi.com · manuals.plus · www.hotwater.com · www.manualshelf.com · www.manualslib.com · www.manualshelf.com · www.manualslib.com · www.manualslib.com · manuals.plus · www.hotwater.com