Rheem Tankless Water Heater Flashing 11

The Short Answer: Rheem tankless 11 is ignition failure: the board tried, did not prove flame, lockout. Gas cock closed, lazy spark, dirty flame rod, empty LP, or a dead thermal fuse — not a full code chart. Photograph it. Fix the obvious cause. Reset once. Do not measure gas pressure yourself. Do not keep cycling a flooded burner. Electric Rheem tankless E-codes are a different machine.

Search Intent & The Real Problem

The remote or the PCB LED is flashing 11. The shower died. This is Paloma-based Rheem gas tankless — RTG, RTGH, Performance, EcoSense, and many indoor/outdoor twins — not a tank Rheem with a status light. 11 never lit. 12 lit, then lost flame (same split as Rinnai 12 and Takagi 111). 14 is thermal fuse / overheat. Do not treat a 13 remaining-flame or a packed inlet screen that never calls for fire as 11.

A cold tank Rheem is not heating. Mid-shower dropout without a code is often min-flow — tankless goes hot to cold.

What other guides get wrong

They paste the entire 10/11/12/14/16 table into an 11 article. They tell you to reset until it fires. Ten resets glaze the igniter. They send homeowners at a manometer. They confuse 11 (never lit) with 12 (lit, then died) and with a packed inlet screen that never calls for fire. And they “fix” 11 by descaling first — scale is 14/16 territory until proven otherwise. Steel-wool-the-rod-every-weekend is how you buy a new rod.

Step-by-Step Troubleshooting

Step 1: Photograph 11 vs 12 vs 14 — then stop guessing

• What to look for: Two digits on your remote or 7-seg LED, flashing. Model on the rating plate (RTG-64/84, RTGH-90/95, Paloma-badged twins). Electric tankless (RTE / RTEX class) uses E-codes, not 11.
• Required tools: Phone photo of the code before you kill power. Reset is last, not first — same discipline as a Takagi reset.

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

• What to look for: Appliance shutoff handle parallel to the pipe (open). Other gas appliances lighting. LP bottles not empty; a cold first-stage regulator frosting on a 20°F morning will 11 a unit that was fine in July. 1/2” flex on a 160–199 kBTU Rheem is a starvation install — it lights the stove and will not light this. New install or a meter relight in the last day can be air in the line. That is a licensed purge and leak test, not a union crack.
• 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. at the appliance — confirm the rating plate, never by ear).

Step 3: Spark at the igniter — one look through the sight glass

• What to look for: Cover on. One hot-water call. Blue-white snap at the electrode through the sight glass, then gas, then flame. No spark = igniter, high-voltage lead, PCB fuse. Spark, no flame = gas path (step 2) or a burner full of dust/spider silk on an outdoor unit. Brief flame, then 11 = flame rod did not prove (step 4). A bang is delayed ignition — shut it down, not a second trial. Rain in the cabinet: dead after rain.
• Required tools: Ears and eyes. One trial. Do not run it with the cover off “to see better.”

If the combustion fan is silent on a call, stop. A dead blower is CO risk — blower not working. Exhaust odor indoors is not an 11 you reset through — tankless exhaust smells like gas.

Step 4: Flame rod, hi-limit, thermal fuse — safeties that fake a dead igniter

• What to look for: Flame rod sooted so the board never sees ionization (often a few microamps when healthy — a licensed reading). Hi-limit / overheat button on many cabinets: power off, press until it clicks. If it trips again, that is overheat or a failed limit — not another 11 reset. 14 is the one-shot thermal fuse around the exchanger; an open fuse can refuse ignition. PCB glass fuse blown after a wet leak — find the leak first. Inlet screen grit causes no-fire without an 11 more often than it causes 11; do not descale an 11 as step one.
• Required tools: Power off before you touch a hi-limit. A light wipe on a cool rod is the most a homeowner should do. Do not sandpaper it as a lifestyle. Do not bend the gap. Do not jumper the thermal fuse.

An 11 with a flame you can see is almost never “no gas.” It is sense, wiring, or the board.

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

• What to look for: Cause addressed (cock open, LP in the bottle, termination not packed with snow, fan spinning). Remote ON/OFF off 10–30 seconds, on — or kill the appliance switch the same way. Unit fires in the trial window, stable flame, no bang, no 11 return. Same 11 on the next shower is the end of DIY.
• Required tools: Your hand on the switch. No paperclip in the PCB.

House static over ~80 psi and a dumping T&P (150 psi / 210°F typical) is pressure, not 11. A tankless that never tries because flow is a trickle is tankless pressure drop, not this code.

When DIY Ends: Calling a Licensed Pro

Stop at gas odor, delayed-ignition bangs, a 13, a hi-limit that will not stay reset, an open thermal fuse, a silent fan, a wet board, and any gas-pressure or gas-valve work. You may photograph the code, confirm the shutoff, look for spark through the glass, press a hi-limit once with power off, and power-cycle once. Combustion, manometer, igniter/flame-rod replacement inside the burner, and PCB work are licensed. Rheem will not smile on an igniter you reset through a flooded burner all weekend.

Frequently Asked Questions

Q: What does flashing 11 mean on a Rheem tankless water heater? A: Ignition failure. The board did not prove flame in the trial. 12 is flame loss after a successful light. 14 is thermal fuse / overheat. Electric Rheem tankless units do not use code 11.

Q: How do I clear a Rheem tankless code 11? A: Photograph the code, fix the obvious cause (gas cock, LP, one spark look, vent 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.”