Rheem Tankless Error Code E5: Meaning, Causes & Fix

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 — EcoSmart is Rheem's electric tankless division — lists E5 simply as 'high flow rate': a capacity report, not a failed part.

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.

What causes the E5 code on a Rheem water heater?

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.

High-flow fixtures without restrictors

Rain heads, body-spray panels, and older unrestricted showerheads can pass more water than a mid-size electric tankless can heat at winter inlet temperatures, all by themselves. The same applies to a tub filler run wide open. Fitting a modern flow-restricting showerhead or aerator sized to the heater's capacity is the standard correction, and most users find the shower experience unchanged — the restrictor removes flow the heater could not heat anyway, so what remains arrives at full set temperature.

One breaker circuit off, shrinking the element bank

Large electric tankless units are fed by multiple breaker circuits, each powering part of the element bank. If one breaker is off or has tripped — after panel work, a surge, or an overload — the heater runs on partial power and its flow ceiling drops proportionally, so E5 appears at flows it used to handle easily. Checking that every breaker labelled for the water heater is on is a documented early check for this code, and it costs nothing but a walk to the panel.

Winter inlet water demanding a bigger temperature rise

The ceiling is set by temperature rise as much as by flow. Water entering at summer temperatures might need a modest lift to reach the set point; the same unit fed with near-freezing winter groundwater must add far more heat to every gallon, so its maximum servable flow can fall dramatically. An E5 that arrives with the cold season and leaves in spring, on a unit that has not changed, is usually this — the heater is honestly reporting seasonal physics.

Unit genuinely undersized for the home

Sometimes E5 is a sizing verdict: the home has gained a bathroom, a soaking tub, or occupants since the heater was chosen, or the unit was marginal from the start. Every check passes — breakers on, fixtures reasonable, flow moderate — and the code still posts at combined draws. The corrections are structural: serve one high-demand fixture with a small point-of-use heater, or replace the unit with a higher-capacity model (an electrician and plumber job, since larger units often need heavier wiring and breakers).

Checks to run before you replace anything

1. 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.
2. Repeat with fixtures added one at a time and note exactly which combination triggers E5 — that threshold is the key fact for any fix or sizing decision.
3. Check the breaker panel: every circuit feeding the water heater should be on. These units commonly use two to four breakers; one off is a hidden capacity cut.
4. Look at your showerheads and faucets for flow rates; a rain head with no restrictor is a prime suspect. Try a restrictor or a lower-flow head as a test.
5. Clean the inlet filter/screen on the cold inlet if your model has one — while a clog restricts flow rather than raising it, a fouled screen disturbs the flow sensing the control relies on.
6. Test the inlet-valve trick: partially close the cold inlet valve slightly and run the problem fixture. If full temperature returns, the heater is healthy and flow was the whole story.
7. Note the season and your incoming water temperature if you know it — a winter-only E5 on an unchanged home points at temperature rise, not at a dying heater.

How to fix rheem water heater error code e5?

1. Reduce simultaneous demand: stagger the big draws (laundry, tub, showers) until you know the unit's comfortable ceiling.
2. Fit aerators on faucets and a flow-restricting showerhead matched to the heater's capacity on the highest-flow fixtures.
3. Restore full power: switch any tripped or off water-heater breaker back on; if a breaker trips again, stop and call an electrician — repeated tripping is a fault, not a nuisance.
4. Use the inlet valve as a temporary trim only: slightly closing it proves the diagnosis and can carry a single fixture, but the proper fix is restrictors at the fixtures so the rest of the home keeps normal pressure.
5. If E5 persists at modest, single-fixture flow with all breakers on, book service to check the flow sensor and element bank — an element section can fail silently and cut capacity.
6. For a chronically undersized installation, get quotes for a point-of-use booster at the worst fixture or a higher-capacity unit with the electrical upgrade it needs.

The part that usually fails: Aerators and flow restrictors

The 'part' that fixes most E5 codes costs a few dollars and screws on by hand. A faucet aerator or an inline shower restrictor limits a fixture to a set flow — so the fixture can never ask the heater for more than it can deliver at temperature. Sizing is the whole game: choose restrictors that bring your biggest fixtures inside the heater's rated flow at your winter temperature rise, and the shower still feels strong because every gallon that passes arrives fully heated instead of diluted lukewarm. Fit them at the fixtures rather than throttling the heater's inlet valve, so pressure elsewhere in the home stays normal.

Rheem electric tankless water heater e5 error code reset

E5 is a live condition code, not a latched lockout, so there is usually nothing to reset: reduce the flow into the unit's range and the display clears and full temperature returns as soon as the outlet recovers. If the display seems stuck after flow has been cut back, turn the hot water off, switch the unit's breakers off for a minute, switch them back on, and retest with a single low-flow tap. EcoSmart's troubleshooting guidance for E5 is entirely about correcting flow — no button sequence is documented for this code, and none is needed. An E5 that reappears immediately at genuinely low flow is no longer a flow problem: treat it as a capacity fault (element bank or flow sensing) and book service.

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.

Why does the E5 code keep 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.

How to stop E5 coming back

• 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.
• High-flow fixtures without restrictors: Rain heads, body-spray panels, and older unrestricted showerheads can pass more water than a mid-size electric tankless can heat at winter inlet temperatures, all by themselves. The same applies to a tub filler run wide open. Fitting a modern flow-restricting showerhead or aerator sized to the heater's capacity is the standard correction, and most users find the shower experience unchanged — the restrictor removes flow the heater could not heat anyway, so what remains arrives at full set temperature.
• One breaker circuit off, shrinking the element bank: Large electric tankless units are fed by multiple breaker circuits, each powering part of the element bank. If one breaker is off or has tripped — after panel work, a surge, or an overload — the heater runs on partial power and its flow ceiling drops proportionally, so E5 appears at flows it used to handle easily. Checking that every breaker labelled for the water heater is on is a documented early check for this code, and it costs nothing but a walk to the panel.

Retrieving stored fault 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.

Other Rheem water heater error codes

See the full list on the Rheem Water Heater error codes hub.

Codes E5 gets confused with

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.

29 — Rheem tankless, and the meaning depends on generation. On condensing IKONIC-era models: condensation is not draining from the collector — the built-in drain trap's electrode reports the trap full or unreadable. On RTGH condensing models the service chart says the neutralizer is clogged. On older RTG and Rheem Australia models, 29 meant heat exchanger outlet temperature too low. Identify your model before acting. 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.

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.

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