Rheem Tankless Error Code 11: No Ignition — Meaning, Causes & Fix

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.

What causes the 11 code on a Rheem water heater?

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.

Gas filter at the gas connection blocked

There is a small filter in the gas connection at the bottom of the heater, and Rheem's manual calls it out specifically for this code: if the gas filter is blocked by some foreign substance, clean the filter and remove the blockage. Debris from new pipework, thread sealant, or dirt in an older line collects there and starves the burner at exactly the moment it needs full flow. Accessing it means breaking a gas connection, so for most owners this is a technician item — but it explains an 11 that appears right after gas work.

Gas pressure too low under load (dynamic pressure sag)

Rheem specifies 4.0-10.5 in. W.C. for natural gas and 8.0-13.0 in. W.C. for LP, and warns that while static pressure is normal, another gas appliance running can cause a drop at the water heater — which is why the manual requires a dynamic pressure check at maximum combustion. An undersized gas line, a failing regulator, or a long run shared with a furnace can pass at idle and fail at light-off. This is the classic cause of an 11 that only appears when the furnace or range is also running.

Blocked or disconnected venting

The control proves airflow before it will complete ignition, so a vent termination plugged with a nest, snow, or debris — or a vent joint that has come apart — can stop the sequence and log 11. Rheem's instruction is to check the condition of the venting, including connections and termination, on both the inlet and exhaust sides, reconnect anything disconnected, and clean the termination. Walk outside and look at both terminations before assuming an internal part has failed; this cause costs nothing to find.

Igniter rod, flame rod, or control board fault

If gas and air are both present, the fault moves to the sensing chain: an igniter rod or coil that produces no spark (checkable through the sight glass), a flame rod coated in combustion deposits that cannot pass its proving current even with a healthy flame, loose connectors, or a control board that has stopped driving the sequence. Rheem's flow chart works through reseating connectors, cleaning the rods, and replacing the igniter coil, flame rod, or board in that order — all internal work for a technician.

Checks to run before you replace anything

1. Confirm other gas appliances in the home (stove, furnace) light and run normally — this separates a house supply problem from a heater problem.
2. Look at the gas shut-off valve on the pipe at the heater: the handle should be fully in line with the pipe, not part-turned.
3. If the home uses LP/propane, check the tank gauge before anything else — an empty or nearly empty tank is a textbook cause of 11.
4. Walk outside and inspect both vent terminations (intake and exhaust) for nests, leaves, snow, or insect blockage, and confirm no vent section has slipped apart.
5. Check the air intake area around the unit is clear and the inlet screen/filter is not clogged with dust or lint.
6. Listen and, where a sight glass is fitted, watch during a hot-water call: repeated clicking with no burner roar points to ignition failing, which is useful information for a technician.
7. Make one documented reset attempt only (see the reset steps below) after the checks above — repeated resets against an unfixed cause help no one.

Rheem tankless water heater error code 11 fix

1. Open the gas shut-off valve at the heater completely, and restore any interrupted supply (refill or replace the LP tank if it is empty).
2. Clear any blockage at the intake and exhaust terminations and reconnect any vent section that has come apart.
3. Clean the air inlet screen/filter if it is fouled.
4. Run the documented reset once: close the hot tap, turn the controller off, switch off the electrical supply, wait 5 minutes, restore power, turn the controller on, and open a hot tap.
5. If the code returns, stop: spark, gas pressure, gas filter, and flame-rod diagnosis involve gas connections and combustion components — book a licensed technician and tell them the code is 11 and what you already checked.
6. If you ever smell gas at any point, do not reset anything: leave the area and call your gas utility from outside.

The part that usually fails: Flame rod

The flame rod is a slim metal probe mounted at the burner, positioned so its tip sits in the flame when the burner lights. It proves combustion electrically: the control passes a small current through the flame to the rod (flame rectification), and only a real flame completes that circuit. Combustion deposits gradually coat the rod and insulate it, which is why Rheem's diagnostic flow has the technician remove and clean the rod before replacing anything. A rod that is cracked, heavily corroded, or still not proving flame after cleaning is replaced — a modest part, but fitting it means opening the combustion side of the heater, so it is technician work.

Rheem tankless water heater error code 11 reset button

Rheem documents two clearing routes. The Use and Care procedure for RTGH models: close the hot water faucet, turn the remote control off, wait 5 minutes, turn it on again, and open a hot water faucet — if the code is still displayed, close the faucet, turn the unit off, and call for service. Rheem Australia's continuous-flow guide adds switching off the electrical supply during the 5-minute wait and confirming the gas isolation valve is fully open before restarting. On IKONIC models, the built-in display clears alarms through ENTER, then answering Yes to 'Clear Alarms?'. One reset after fixing the likely cause is the documented pattern; a code 11 that returns immediately has a live fault — gas, venting, or a sensing part — and resetting it again changes nothing.

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 11 code keep 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.

How to stop 11 coming back

• 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.
• Gas filter at the gas connection blocked: There is a small filter in the gas connection at the bottom of the heater, and Rheem's manual calls it out specifically for this code: if the gas filter is blocked by some foreign substance, clean the filter and remove the blockage. Debris from new pipework, thread sealant, or dirt in an older line collects there and starves the burner at exactly the moment it needs full flow. Accessing it means breaking a gas connection, so for most owners this is a technician item — but it explains an 11 that appears right after gas work.
• Gas pressure too low under load (dynamic pressure sag): Rheem specifies 4.0-10.5 in. W.C. for natural gas and 8.0-13.0 in. W.C. for LP, and warns that while static pressure is normal, another gas appliance running can cause a drop at the water heater — which is why the manual requires a dynamic pressure check at maximum combustion. An undersized gas line, a failing regulator, or a long run shared with a furnace can pass at idle and fail at light-off. This is the classic cause of an 11 that only appears when the furnace or range is also running.

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 11 gets confused with

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.

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.

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.

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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