Rheem Tankless Error Code 29: Meaning, Causes & Fix

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. 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.

What causes the 29 code on a Rheem water heater?

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.

Drain line blocked or pinched

The condensate line runs from the trap to a floor drain, sink tailpiece, or condensate pump, and anything that stops it stops the heater: a kink where the flexible line bends, a line crushed behind the unit, algae and sludge growth in a slow line, or debris at the outlet. Rheem's instruction is to check the drain line for internal or external blockage and make sure it is not pinched. This is the most common cause on established installations and the most owner-tractable: trace the whole run with your eyes and hands before calling anyone.

A P-trap fitted to the drain line (double-trapping)

Well-meaning installers sometimes add a P-trap to the condensate line out of plumbing habit. Rheem states plainly that the drain line does not need a P-trap because the unit has a built-in trap, and instructs: if the drain line has a P-trap, remove it. Two traps in series airlock the line, condensate backs up to the electrode, and 29 appears on a system where nothing is actually blocked. If your line visibly dips into a U-bend between the heater and the drain, this is very likely your code.

Neutralizer clogged or media exhausted (RTGH condensing generation)

On RTGH condensing models the service chart defines 29 as a clogged neutralizer. The neutralizer canister holds limestone-type media that neutralises acidic condensate as it passes; as the media dissolves and fouls, flow through it chokes until condensate backs up. Rheem charts the lifecycle openly: 92 warns replacement is due soon while the unit still runs, 93 says the neutralizer must be replaced and the unit cannot be used. A 29 on an RTGH with an old neutralizer is the same story told from the blockage side — plan on media or canister replacement.

Frozen drain line, or a failed trap electrode

In an unheated garage or a cold snap, a shallow or exterior run of condensate line can freeze solid; the trap fills from the burner side and 29 posts even though nothing inside the heater is wrong. The rarer internal cause is the level electrode itself: scaled, fouled, or disconnected, it reports 'full' or 'unknown' regardless of the real level — which is why Rheem's wording covers both a trap that is full and a trap whose level cannot be detected. Electrode and wiring faults are the technician end of this code.

Checks to run before you replace anything

1. 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.
2. Trace the entire drain line to where it terminates, feeling for pinches, kinks, or crushed sections, especially behind the heater.
3. Look for a P-trap or deep U-bend in the line — Rheem says the line must not have one, because the trap is built into the unit.
4. Check the line's outlet: is it submerged, blocked with debris, or frozen? In cold weather, check the full run for ice, particularly any section in an unheated space.
5. If your unit has a condensate pump, confirm the pump has power and its reservoir is not full or fouled.
6. On RTGH condensing models, check the neutralizer: note its age and whether a 92 warning appeared in the past — that was the early notice.
7. Look for water: drips under the unit or a wet trap area tell you condensate really is backing up, rather than the electrode guessing.

Rheem water heater error code 29 how to fix

1. Remove the protection plug from the drain connection at the bottom of the unit if it is still fitted.
2. Clear the drain line: straighten pinches, flush or replace a sludged section, and clear the outlet at the drain.
3. Remove any P-trap from the condensate line and re-run the line with a continuous gentle fall to the drain, as Rheem instructs.
4. Thaw a frozen line gently (warm room air or warm towels — never a flame) and insulate or re-route the vulnerable section.
5. On RTGH models with a clogged or exhausted neutralizer, replace the media or canister; treat a preceding 92 as the scheduling warning it was.
6. Reset the unit once the drain path is proven clear (controller off, power off, 5 minutes, restore, open a hot tap). If 29 returns with a visibly free-flowing line, the trap electrode or its wiring needs a technician.

The part that usually fails: Condensate drain trap and neutralizer

Condensing models carry two parts owners rarely meet until 29 introduces them. The built-in drain trap collects condensate from the secondary heat exchanger and holds a water seal that keeps exhaust gas out of the drain line; a level electrode in the trap reports to the control, and that electrode's report is code 29. Downstream, many installations add a neutralizer — a canister of alkaline media that treats the acidic condensate before it reaches household drainage; on the RTGH generation, Rheem ties 29 (and end-of-life codes 92 and 93) directly to this canister. Trap cleaning and line work are owner-manageable; neutralizer media replacement is simple but messy, and many owners hand it to the service technician at the annual visit.

Rheem tankless water heater error code 29 reset

There is no separate button ritual for 29: clear the condensate path first, then use Rheem's standard documented clearing procedure — close the hot water faucet, turn the remote or built-in controller off, switch off the electrical supply, wait 5 minutes, restore power, turn the controller on, and open a hot tap. On IKONIC models the display also offers ENTER followed by Yes to 'Clear Alarms?'. The electrode re-reads the trap continuously, so if drainage is genuinely restored the code stays clear; if the line still cannot drain, 29 will post again as soon as condensate rebuilds — minutes to hours of burner run time — which is itself a useful confirmation that the blockage is still there.

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 29 code keep 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.

How to stop 29 coming back

• 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.
• Drain line blocked or pinched: The condensate line runs from the trap to a floor drain, sink tailpiece, or condensate pump, and anything that stops it stops the heater: a kink where the flexible line bends, a line crushed behind the unit, algae and sludge growth in a slow line, or debris at the outlet. Rheem's instruction is to check the drain line for internal or external blockage and make sure it is not pinched. This is the most common cause on established installations and the most owner-tractable: trace the whole run with your eyes and hands before calling anyone.
• A P-trap fitted to the drain line (double-trapping): Well-meaning installers sometimes add a P-trap to the condensate line out of plumbing habit. Rheem states plainly that the drain line does not need a P-trap because the unit has a built-in trap, and instructs: if the drain line has a P-trap, remove it. Two traps in series airlock the line, condensate backs up to the electrode, and 29 appears on a system where nothing is actually blocked. If your line visibly dips into a U-bend between the heater and the drain, this is very likely your code.

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 29 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.

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.

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 — 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.

Frequently asked questions

Related guides

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