Rheem Water Heater Error Codes List: Every Code Explained

Every Rheem water heater error code we could verify against Rheem's own documentation — what it means, what usually causes it, and the first fix to try — in one table. Codes differ between model series, so treat your model's tech sheet as the final word.

How to read and retrieve error codes on Rheem water heaters

Rheem water heaters report faults in three separate languages, and reading the right one is the whole skill. A tank gas heater with an electronic combination gas control has no screen: a single status LED on the control blinks in patterns — 1 flash for normal operation, and 2, 4, 5, 7 or 8 red flashes for faults (Rheem's chart deliberately has no 3- or 6-flash entries). Power-vent models on the IntelliVent control instead use lettered LEDs (A-F) as temperature indicators and error displays. Gas tankless models (RTGH, RTG, IKONIC) show two-digit numeric codes on a built-in display or remote — 11 for no flame detected, 12 for flame lost, P1 for low flow, 1L for scale — and IKONIC units keep a scrollable fault history of recent faults. Hybrid heat-pump and EcoNet smart electric models speak in alphanumeric alarms: press Next until 'Current Alarm' appears, then scroll with the Down arrow; A-codes are shutdown alarms, T-codes are alerts. Electric tankless models on the RTEX/EcoSmart platform use short E-codes (E1-E5). Always identify the platform before looking a code up: the same characters mean different things in different languages.

The complete Rheem water heater error code list

How to reset / clear error codes on Rheem water heaters

Each Rheem platform resets the way its manual documents, and only that way. Tankless models: close the hot faucet, turn the controller off, switch off the electrical supply, wait 5 minutes, restore power, turn the controller on, and open a hot tap; IKONIC displays also clear alarms via ENTER and 'Clear Alarms?' — Yes; hard lockouts (10, 13, 99) have a DIP-switch procedure that ends with the remote flashing CL (fault history cleared) or UL (reset confirmed). Tank gas controls have no reset button: the status LED clears when the underlying fault clears, and Rheem's chart routes 4, 5, 7 and 8 flashes straight to a qualified technician. Hybrids and smart electric tanks: read and note the alarm first (Next / Down arrows on the hybrid display), fix the cause, then clear; a leak alarm such as A107 can be overridden for 24 hours only by holding Clear Alarm for 5 seconds — time bought to arrange the repair, not to skip it. One reset after fixing the cause is the documented pattern on every platform; repeated resets against a live fault are not a strategy.

How to diagnose any Rheem 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.

Three display languages under one brand

The single most useful fact about Rheem water heater codes is that the brand speaks three unrelated languages, and a code is meaningless until you know which language your heater speaks. Tank gas heaters with the electronic combination gas control have no display: a single LED blinks a count — one flash is health, seven is a dead control. Tankless heaters show two-digit numbers with decimal-family meanings (11 and 12 are the flame pair; 92 and 93 are neutralizer life). Hybrids and smart electrics show letter-number alarms where A005 can mean a compressor discharge trip on a heat-pump model or an element fault's neighbour on a commercial tank — and where the same number on a different platform is not a variation but a completely different sentence. Before searching any code, name your platform out loud: tank gas blink, tankless numeric, hybrid/EcoNet alarm, or electric-tankless E-code. Half of all wrong internet answers about Rheem codes come from reading the right code in the wrong language. That is why the hub table for this brand prints the platform inside every row's meaning: five seconds spent naming the platform saves hours spent chasing the wrong system's fault.

Alarms, alerts, and warnings are not the same word

Rheem's newer platforms grade their messages, and the grade tells you how to respond. On hybrid and Triton models, codes beginning with A are alarms: the heater has shut something down — a compressor, an element, or the whole unit — and will stay shut down until the cause is fixed. Codes beginning with T are alerts: the heater still runs, but it is telling you something is drifting (a flame rod degrading, a filter due for cleaning, demand outrunning recovery). Tankless models draw the same line between error codes, which stop the unit, and warning codes such as 05, 07, 10, 48, 49 and 88, which flag conditions — maintenance due, a sensor not installed, leak detection disabled — while heating continues. Read the grade before the number: a T-code or warning is a scheduling task, an A-code or error is a stop-and-fix task, and confusing the two either creates panic over a filter reminder or complacency about a disabled heater. When you report a code to a technician or a parts desk, report the grade with it: an A-code sends the conversation toward a shutdown diagnosis, a T-code toward maintenance — correctly different directions.

The fault history is the diagnosis you already paid for

Rheem's tankless controls remember. The IKONIC-era troubleshooting manual documents a maintenance mode in which position *E shows the error codes of the most recent 8 faults, and the fault history can be verified as cleared (reading NULL at location 1E) after the reset procedure. Hybrids similarly hold current alarms behind the Next/Down display sequence. This memory is gold for intermittent faults: a heater that shows 12 today and nothing tomorrow has still told you it was losing flame, and a repeating cycle of 11-then-12 points at a supply that fails progressively rather than two unrelated faults. Before resetting anything, write down what is displayed, and scroll the history if your model offers it. Resetting first and reading later throws away the only evidence an intermittent fault leaves behind — which is why Rheem's own procedures put reading and recording ahead of clearing. A dated phone photograph of the display is the simplest fault log there is, and a series of them across a season is often what finally convinces a technician — or a warranty desk — that a fault is real, recurring, and patterned.

The most searched Rheem water heater codes, in detail

11 — Rheem tankless (RTGH / RTG / IKONIC): flame not detected by the flame rod. At ignition the unit tries to light twice, and if the flame rod never proves a flame, it shuts down and displays 11. The RTGH service chart gives the classic owner-level cause: the gas shut-off valve is not fully opened.

A Rheem tankless heater lights in a strict sequence. A hot tap opens, the flow sensor reports water moving, the blower runs a pre-purge to clear the combustion chamber, the gas valve opens in stages, and the igniter rod throws a visible spark at the burner — on these units you can watch for that spark through the sight glass. Lighting the gas is only half the job: a separate metal probe, the flame rod, sits in the flame and proves it is really burning by passing a tiny electrical current through the flame itself, a principle called flame rectification. Rheem's Tankless Troubleshooting Manual (AP21822) is precise about code 11: in the case of ignition failure, the water heater will attempt ignition 2 times, and if no flame is detected it displays 11 on the built-in controller or the remote controller. So an 11 means the sequence ran but proof of flame never arrived — either there was no spark, no gas to light, or a flame the rod could not sense. The manual's diagnostic check items for 11 are gas supply pressure, venting, the gas filter, the igniter rod, the flame rod, and the DIP switch settings. Correct supply pressure at the unit is 4.0 to 10.5 inches of water column for natural gas and 8.0 to 13.0 for LP, and Rheem stresses checking both static pressure (unit idle) and dynamic pressure (unit at maximum combustion), because pressure that looks fine at rest can sag when the burner and other appliances draw together. The simpler RTGH service chart in the Use and Care manual puts the most common real-world cause first: gas shut-off valve not fully opened — open it completely. Blocked or disconnected venting also causes 11, because the blower cannot establish the airflow the control expects before and during ignition. Code 11 is a lockout-style fault: the heater will not produce hot water until the cause is corrected, and repeated blind resets simply repeat two failed ignition attempts against a fault that has not changed. The same code appears in Rheem Australia's continuous-flow fault list as 'ignition failure at start up', which is why the diagnosis in this article follows the order all of Rheem's documents share: fuel first, air second, sensing third.

Most likely cause: Gas shut-off valve not fully open, or gas supply interrupted — Rheem's own RTGH service chart lists this first for code 11, and it is the most common cause in practice: a valve left half-open after plumbing work, a meter or supply interruption, or an LP tank that has run empty. The igniter can spark perfectly and the unit still shows 11, because there is simply nothing to light. Check that the valve handle at the heater is fully parallel to the pipe, confirm other gas appliances in the home work, and check the LP tank gauge if you heat with propane.

First check: Confirm other gas appliances in the home (stove, furnace) light and run normally — this separates a house supply problem from a heater problem.

If it keeps coming back: Code 11 returns when the underlying condition was never actually removed. A half-open valve gets nudged, works for a week, and drifts; a gas filter that caught debris once keeps catching it until the line is cleaned; an LP tank that 'still had a little in it' runs dry on the coldest night; a flame rod cleaned as a guess fouls again because the real problem was low dynamic pressure making a weak, poorly anchored flame. Treat a second 11 as data: note what else was running in the house and whether the vent terminations were clear, because that pattern is what the technician needs.

12 — Rheem tankless (RTGH / RTG / IKONIC): flame detected, then lost. The burner lit and the flame rod proved flame, but the flame dropped out during operation; Rheem's manual states the unit counts these flame-loss incidents and displays 12 after 3 consecutive losses. The RTGH service chart gives the plain-language causes: gas service interrupted, or LP gas running low.

Code 12 begins where code 11 ends. The ignition sequence succeeded — the flame rod proved a real flame — and the heater settled into heating. Then, mid-run, the flame signal vanished. Rheem's Tankless Troubleshooting Manual (AP21822) describes the behaviour exactly: if the water heater detects loss of flame during combustion, it stops supplying fuel, attempts to restart, and counts the incidents of flame loss; if the incident occurs 3 times consecutively, the unit displays 12 on the built-in controller or the remote. That counting matters for diagnosis: a single gust or a one-off pressure dip produces a restart you may never notice, while a 12 on the display means the flame is failing repeatedly and predictably. The causes sit in three groups. First, fuel delivery that degrades while running: LP gas running low (the RTGH chart names it directly), a gas service interruption, a gas filter at the heater's connection slowly strangling flow, or dynamic pressure sag when other appliances draw on the same line. Second, flame sensing that degrades: a flame rod coated in deposits may prove a strong flame at light-off yet drop the weaker or shifting signal mid-burn, and Rheem's diagnostic flow for 12 is built around cleaning and testing that rod. Third, combustion air: venting that is partly blocked or a termination exposed to gusts can disturb the flame until it lifts off the burner. The diagnostic check items Rheem lists for 12 are the same family as 11 — gas supply pressure (4.0-10.5 in. W.C. natural gas, 8.0-13.0 in. W.C. LP, checked dynamically), venting, gas filter, flame rod, and DIP switch settings — because the two codes share hardware and differ mainly in when the flame proof fails. A heater showing 12 usually still delivers some hot water in bursts between shutdowns, which is a useful symptom to report: cold bursts mid-shower with a 12 on the controller is the signature of flame loss under way, not a dead unit. Rheem Australia's chart compresses the same fault into four words — 'flame failure during operation' — and its owner-level remedies sit at the fuel end of the system, which matches field experience: most 12s are born in the supply or the sensing, not in the burner itself.

Most likely cause: LP gas running low, or gas service interrupted — Rheem's RTGH service chart reduces code 12 to two owner-level causes: gas service interrupted — contact the gas utility — or LP gas running low — refill or replace. A propane tank near empty delivers falling pressure exactly as demand rises, so the burner lights on what pressure exists and then starves. This is the first thing to check on any LP installation, and the cheapest: read the tank gauge before booking anyone. A tank showing a quarter or less in cold weather is effectively empty for a high-draw appliance, because the liquid vaporises more slowly as its temperature falls.

First check: If the home runs on LP/propane, read the tank gauge first — Rheem's own chart puts 'LP gas running low' at the top of this code's causes.

If it keeps coming back: Code 12 is a pattern code, so it comes back in patterns. Fill the LP tank and it vanishes until the tank runs low again. Clean the flame rod without fixing a pressure sag and it returns on the first cold morning the furnace runs hard. Clear a vent termination and it returns when the nest is rebuilt. The count-to-three behaviour also means the fault can simmer invisibly — single flame losses, silently restarted — before it ever displays. If your household notices unexplained cold bursts in the shower, treat that as early 12 behaviour and get the supply and rod checked before the lockouts start.

29 — Rheem tankless, and the meaning depends on generation. On condensing IKONIC-era models: condensation is not draining from the collector

A condensing tankless heater squeezes extra heat from its exhaust, and the price of that efficiency is water: vapour in the flue gas condenses inside the secondary heat exchanger and must drain away continuously while the burner runs. Rheem's current condensing design collects that condensate in a built-in drain trap, and the trap is supervised — Rheem's Tankless Troubleshooting Manual (AP21822) explains that if the electrode on the drain trap detects the water level is full, or cannot detect the water level in the trap, the heater displays 29 on the built-in or remote controller and stops. It is a protective stop: a trap that cannot drain will eventually back condensate into places it can damage, and acidic condensate is not something the heater will let pool inside itself. The manual's diagnostic items are short and physical: the drain connection on the trap, and the drain line. Two installation leftovers cause a large share of 29s on newer units — the protection plug on the drain connection at the bottom of the unit was never removed, so condensate has nowhere to go from day one; and the drain line has been fitted with a P-trap, which Rheem explicitly says the line does not need and instructs to remove, because the unit already contains a trap. A pinched or blocked drain line, or a frozen line in an unheated space, produces the same code on older installations. On the previous RTGH condensing generation the chart expresses the same physics from the neutralizer's side: 29 means the neutralizer — the canister of media that treats the acidic condensate — is clogged, and its companions 92 (neutralizer replacement due soon, unit usable) and 93 (neutralizer must be replaced, unit unusable) chart the media's end of life. Only on the older non-condensing RTG generation and in Rheem Australia's chart does 29 carry a different meaning entirely — heat exchanger outlet temperature too low, fixed by cleaning the air inlet screen and heat exchanger fins. Same number, three adjacent stories, all documented by Rheem: the constant thread is that 29 is about the condensate path on any condensing model.

Most likely cause: Protection plug left in the drain connection — Rheem's manual flags this in a formal notice: the protection plug on the drain connection may not have been removed, and it must be taken out of the connection at the bottom of the unit. Shipping plugs exist to keep debris out during installation; if the installer missed it, the trap has been sealed since day one and the first real condensate load fills it. This is the prime suspect on any unit that shows 29 in its first season, and the fix is literally pulling a plug — though access and confirmation are often easiest for the installer to close out.

First check: Start at the bottom of the unit: find the condensate drain connection and confirm the protection plug was removed and the line is actually attached.

If it keeps coming back: Condensate problems recur on a schedule set by physics. A line cleared of sludge grows it again in a year or two, especially on a slow, flat run. Neutralizer media dissolves by design, so 92, then 29 or 93, return when the new charge is spent. A plug or P-trap problem, once fixed, stays fixed — but a frozen line freezes every hard winter until it is insulated or re-routed, which is why winter-only 29s should be believed rather than reset. And a trap electrode that has posted one false 'full' report through scale fouling will do it again until it is cleaned or replaced.

E5 — Rheem electric tankless (EcoSmart / RTEX platform): high flow rate. The water is moving through the heater faster than its elements can bring it to the set temperature, so the outlet runs lukewarm and the control reports E5. EcoSmart's troubleshooting guide

An electric tankless heater has no stored hot water. Every degree of temperature rise must be added in the seconds water spends inside the heat exchanger, and the elements can only add a fixed amount of energy per second. That physics defines a hard ceiling: at a given incoming water temperature and set point, there is a maximum flow the unit can serve at temperature. Push more water through than that ceiling — a rain shower plus a filled tub, two bathrooms at once, a high-flow fixture with no restrictor — and the same element power is spread across more water, so outlet temperature sags and the control posts E5, which the EcoSmart troubleshooting guide defines as high flow rate. Notice what E5 is not: it is not an overheat (that is E4 on this platform, where outlet temperature runs too high), not a sensor failure (E1 inlet thermistor, E2 outlet thermistor, E3 both), and not an ignition or flame fault — an electric unit has no flame, so the 'E5 means ignition failure' claims circulating on generic code lists are describing some other appliance entirely. E5 behaves like a live measurement rather than a latched fault: throttle the flow back into the unit's range and full temperature returns, which is also the diagnostic test. Anything that lowers the ceiling produces the same code at ordinary flows — winter groundwater demanding a much larger temperature rise, one of the unit's several breaker circuits switched off or tripped so only part of the element bank is powered, or heavy scale narrowing the exchanger. The documented owner responses all work on the flow side of the equation: reduce flow at the fixtures, fit aerators or flow restrictors, and as a test, partially close the inlet valve slightly to see whether full temperature returns at reduced flow — if it does, the heater is healthy and the household demand is simply bigger than the unit. That last point is the honest endpoint of many E5 investigations: the code is the heater accurately reporting that it is undersized for how the home now uses hot water.

Most likely cause: Too many fixtures drawing at once — The classic E5: a shower running while a tub fills, the washing machine's hot fill, and a kitchen tap together exceed what the elements can serve. Each fixture alone is fine; the sum is not. Because the code tracks live flow, it appears at peak moments — mornings, laundry day — and vanishes when demand drops. No part is failing; the household has simply found the heater's ceiling. Staggering draws or trimming fixture flow rates resolves it.

First check: Run one low-flow hot tap alone (a single bathroom faucet with an aerator): if the water reaches full set temperature and E5 stays away, the heater works and the issue is total flow.

If it keeps coming back: E5 returns whenever the balance tips again: a new high-flow showerhead fitted during a bathroom refresh, guests in the house doubling morning demand, a breaker switched off during unrelated panel work and never restored, or the first cold snap dropping inlet temperatures and cutting the unit's effective capacity. Scale building inside the exchanger slowly lowers the ceiling too, so an E5 threshold that creeps downward over years is worth a service visit and a flush. The code is best read as a gauge, not an alarm — when it reappears, ask what changed: demand, power, season, or the unit.

Less common and model-specific codes

Search data shows owners also meet these codes on Rheem water heaters: Heater. They are not part of the core code list Rheem publishes for most models — several are series-specific, abbreviated display readings, or codes carried over from a sister platform — so we do not publish meanings for them rather than guess. Treat them by symptom: note what the machine was doing when the code appeared (filling, draining, heating, spinning), run one full power cycle (5 minutes off), and if the code returns, match the symptom to the closest documented family in the table above and check the tech sheet stored inside your machine for the model-specific definition.

Deep-dive guides for the most searched codes

Related guides

Facts on this page were checked against manufacturer documentation: files.myrheem.com · files.myrheem.com · www.manualshelf.com · www.manualshelf.com · www.manualshelf.com · mans.io · manuals.plus · manuals.plus · manuals.plus