Rheem Code 11: Ignition Failure

The Short Answer: Rheem code 11 on a Paloma-based RTG / RUTG / Prestige tankless is ignition failure: the board tried to light, never proved flame, and locked out. It is not a gas-tank LED count and not electric 5 flashes. Photograph it. Confirm the cock and LP. Reset once. Do not measure manifold pressure yourself.

Search Intent & The Real Problem

The controller or PCB LED says 11. The shower is ice. Google mixed a Honeywell 9-flash, an electric ECO, and a Rinnai 12 into one “code 11” stew. On Rheem, Ruud, and Richmond tankless (Paloma PH / RTG-64 / RTG-84 / RTG-95 / indoor RUTG / many Prestige condensing boxes), 11 is the ignition-failure lockout: spark or HSI ran, flame never proved. 12 is the sister code — it lit, then lost flame. 10 is air/exhaust. A cold Rheem tank with a status light on the gas valve is a different machine.

Sister lockouts: Takagi 111, Rinnai 12, R53 10/11/12. Generic no-flame on a tank: burner not lighting.

What other guides get wrong

They paste the entire 10/11/12/14/16 table into an 11 article and tell you to reset until it fires. Ten resets glaze the igniter and flood the chamber. They send homeowners at a manometer. They treat a Rheem tank 7-flash FVIR as “code 11.” And they skip a closed appliance cock and a 1/2” flex on a 180–199 kBTU burner, so you buy a flame rod for a starvation install.

Step-by-Step Troubleshooting

Step 1: Photograph 11 vs 12 vs 10 — then stop guessing

• What to look for: Digits before you kill power. Rating plate: RTG, RUTG, RTGH, Prestige tankless, Ruud equivalent. Indoor Category III vs outdoor rain cap. A bang on a late light is delayed ignition — loud bang — shut it down, not a second trial.
• Required tools: Phone photo of the code and the plate. No wrenches.

If there is no code and it simply passes cold water, you may have no flow call, not an 11. Packed inlet screen and closed isolation valves never ask the burner to light.

Step 2: Gas cock, other appliances, LP — no manometer

• What to look for: Appliance shutoff handle parallel to the pipe (open). Stove and furnace lighting. LP bottles not empty; a first-stage regulator frosting on a 20°F morning will 11 a Rheem that was fine in July. 1/2” CSST or flex on a 199 kBTU chassis is a starvation install — the range lights, this burner never proves. New meter relight in the last day can be air in the line. That is a licensed purge and leak test, not a union crack. No gas at other appliances is not getting gas, not a board.
• Required tools: Eyes on the cock and the flex. No fittings wrenches.

Inlet and manifold pressure are licensed (NG often ~3.5–7 in. w.c. / LP ~10–11 in. w.c. — confirm the rating plate, never by ear). Fuel DIP or orifice set to the wrong gas after a move is a licensed correction.

Step 3: Igniter, sight glass, one trial

• What to look for: Cover on. One hot-water call. Listen: fan, then spark or glow, then silence and 11. No spark at all: igniter, harness, or board — still not a homeowner gas-valve swap. Spark with a dark burner: fuel never arrived (cock, valve, or empty LP). Brief yellow puff then 11: delayed light or a wet/sooted burner after rain in the cap. Do not run it with the cover off “to see better.”
• Required tools: Ears and eyes. One trial.

A light wipe on a cool flame rod is the most a homeowner should do. Do not sandpaper it into a needle. Microamp flame current is a licensed reading. Repeated 11 with a wet cabinet is a leak first — Rinnai leaking from the bottom is the same physics on a sister Paloma-class box.

Step 4: Vent, wind, and condensate that starve the trial

• What to look for: Outdoor RTG on a windward wall, missing recirc cap, snow over the flue. Indoor RUTG: termination too close to a soffit, long Category III run, or a condensing Prestige with a condensate trap full so the fan never proves air. 10 should have shown first; some boards throw 11 when the trial never sees a stable fire in a bad flue. Bird nest, dryer blowing into the same corner, vinyl intake mashed shut.
• Required tools: Eyes on the cap from the ground. Do not garden-hose the vent.

Clear the exterior. Do not foil a vent joint. A power-vent tank with a dead blower is not a Rheem 11 — blower not working.

Step 5: One reset after the cause — then hire it

• What to look for: Cause addressed (cock open, cap clear, LP not frozen). Power off 10–30 seconds, on. Unit fires, holds flame, no 11 on the next shower. Same 11 on the next call is the end of DIY. Do not descale an 11 as step one — scale is 14/16. Do not hold a tripped breaker On — breaker will not reset.
• Required tools: Your hand on the switch. No paperclip in the PCB.

When DIY Ends: Calling a Licensed Pro

Stop at gas odor, delayed-ignition bangs, an 11 that returns after one reset, a wet board, and any gas-pressure or gas-valve work. You may photograph the code, confirm the shutoff, look at the termination, rinse an inlet screen with water isolated, and power-cycle once. Combustion, manometer, igniter or flame-rod replacement inside the burner, and PCB work are licensed. Rheem will not smile on a rod you reset through a flooded burner all weekend.

Frequently Asked Questions

Q: What does Rheem water heater code 11 mean? A: On Rheem/Ruud tankless, 11 is ignition failure — no proven flame in the trial. 12 is flame loss after it lit. 10 is air/exhaust. A gas-tank LED flash count is a different chart.

Q: How do I reset a Rheem code 11? A: Photograph the code, fix the obvious cause (gas cock, LP, wind at the cap), then power off 10–30 seconds. One reset. An 11 that returns is a licensed diagnosis, not a reset schedule.

Q: Can I check gas pressure on a Rheem 11 myself? A: No. Confirm the shutoff and that other appliances light. Inlet and manifold pressure are a licensed manometer job. Do not loosen fittings to “bleed air.”