Rheem tankless water heater code 11 first means gas is not reaching the burner. Rheem's owner chart says the gas shut-off valve is not fully open, so check that valve and open it all the way, then follow Rheem's reset steps. If 11 comes back, a licensed gas technician checks pressure, venting, the igniter and the flame rod.
Figures checked September 2026. Code meanings from Rheem's Use and Care Manual and technician pocket guide; prices from the dated sources listed at the end.
| Where code 11 comes from | Owner or pro | Cost (source, date) |
|---|---|---|
| Manual gas shut-off valve partly closed | Owner | Free |
| Propane tank low or empty | Owner (refill) | Your propane supplier's price |
| Gas supply pressure low, static or while firing | Licensed pro | Plumbers charge $45 to $150 an hour (HomeGuide, Aug. 2025) |
| Blocked gas filter, air filter or vent | Pro for the cabinet; owner can look at the outside vent | Vent repair $50 to $125 (Fixr, Jan. 2025) |
| Dirty or failed igniter rod or flame rod | Licensed pro | Rheem RTG20329F igniter and flame rod kit $25.66, part only (Rheem Parts, Sept. 2026) |
| Gas-air ratio valve, solenoid valve or control board | Licensed pro | Tankless circuit board $400 to $800 (HomeGuide, July 2025) |
On Rheem's owner chart, code 11 means the gas shut-off valve is not fully opened. The listed fix is to check that valve and open it completely. Most repair pages call 11 an "ignition failure," which is how a technician reads it, but the first thing Rheem asks an owner to check is the gas valve.
The wording comes from Rheem's noncondensing Use and Care Manual, form AP22009 Rev 04, Service Error Code Chart on page 77. The same chart lists 12 as interrupted gas service or low propane, and P1 as too little water flow. Those codes have their own pages: the Rheem tankless P1 code guide and the Rheem tankless code 13 guide.
A closed valve and a failed igniter produce the same result, which is why both descriptions exist: the burner never lights. Rheem's owner chart simply starts with the cause an owner can fix.
Newer Rheem IKONIC condensing models show the code as A011. Rheem's technician pocket guide defines A011 as "Flame Not Detected From Flame Rod": the unit tries to ignite 10 times, with a post-purge every third try, and shows A011 only when no flame was detected. The first owner check, the gas valve, does not change.
That definition is on page 100 of the Tankless Water Heaters Technical Training and Service Manual Pocket Guide, form AP24727, which covers the RTGH-S11i, RTGH-S10i, RTGH-S84i and their SR, CRTGH and RUTGH variants. So a display reading 11 usually points to an older noncondensing Rheem, and A011 to an IKONIC unit. Use the manual that matches your rating plate.
Rheem's manual clears code 11 with the POWER ON/OFF button and, if needed, by unplugging the unit. It has you turn the heater off, wait about five minutes, turn it back on and test a hot tap. If the code stays, you unplug the unit briefly and try once more before calling for service.
Rheem's sequence, from page 76 of the AP22009 Rev 04 manual, with the gas valve check added where the chart points to it:
Rheem's manual adds one more instruction: if a code appears that is not in the chart, turn the heater off right away and call for service.
If the valve is open and gas is available, the cause is inside the heater or its air and gas supply. Rheem's A011 page lists eight checks: gas supply pressure, gas filter, air filter, venting, igniter rod, flame rod, gas-air ratio valve and solenoid valve. Those are technician checks, done with the cabinet open.
The list below follows Rheem's page 100 order. Rheem does not rank them by how often they fail.
For the technician-level readings behind steps 5 to 8, see the Rheem tankless ignition code guide.
An owner can check the gas valve, the propane level, the outside vent and air intake, and the water filter, and nothing inside the cabinet. Rheem's manual tells owners not to repair wiring, gas piping, burners, vent connectors or other safety devices, and not to replace any part it does not specifically name.
Safe checks, all from the Use and Care Manual:
Call a licensed gas technician when code 11 returns after one full reset with the gas valve open, or at once if you smell gas. Everything past the valve involves gas pressure, the burner and 120-volt parts. Rheem's manual warns of shock with the cover off and reserves that work for qualified technicians.
If you smell gas, the manual's first page says not to light any appliance, not to touch electrical switches, and to call your gas supplier from a neighbor's phone. Do not return until the gas supplier or fire department says it is safe.
Also stop if the heater has been flooded or damaged, or if you see scorch marks near the vent. Rheem's manual says to turn off the manual shut-off valve if the heater has been through overheating, fire, flood or physical damage.
Most code 11 calls cost a service visit, and the total depends on whether the fix is a cleaning, a small part or a board. Fixr puts gas tankless repairs at $150 to $650 with labor included (Fixr, January 2025). An open gas valve costs nothing.
| Line item | Figure | Source and date |
|---|---|---|
| Gas tankless repair, labor included | $150 to $650 | Fixr, January 2025 |
| Tankless repair, all types | $300 to $1,300 | HomeGuide, August 2025 |
| Call-out minimum | $50 to $200 | HomeGuide, August 2025 |
| Plumber labor | $45 to $150 per hour | HomeGuide, August 2025 |
| Rheem RTG20329F igniter and flame rod kit, part only | $25.66 (listed as temporarily out of stock) | Rheem Parts, September 2026 |
| Tankless circuit board replaced | $400 to $800 | HomeGuide, July 2025 |
The Rheem Parts listing does not name the models the kit fits, so a technician should match it to the part number in your unit's parts list. No source we could load gives an installed price for a Rheem gas-air ratio valve, so none is shown. For more part prices, see the water heater repair prices guide.
A failed igniter, flame rod, valve or board on a single-family home install is covered as a defective component for 5 years, but Rheem pays labor for only 1 year. A closed gas valve, low gas pressure or an undersized gas line is not a defect, so those fixes are on the owner even when the heater is new.
Rheem's residential tankless gas limited warranty (AP21265 Rev 03) gives 15 years on the heat exchanger, 5 years on component parts and 1 year for certain labor in a single-family home. All warranties end after 12,000 hours of operation. Coverage starts on the documented install date, or else the manufacture date plus 90 days, and is not transferable.
The exclusions matter for this code. The warranty excludes performance problems caused by improper sizing of the gas supply line, the venting connection or combustion air openings, and failures from not maintaining the unit as instructed. It also excludes labor for general service and inspection. Rheem's manual lists its National Service Department on page 77 if a dealer cannot help, and the Rheem repair and warranty guide covers the claim steps.
Repair is the usual call for code 11, because the parts involved are small and the heat exchanger is not part of the diagnosis. Replacement makes sense only when an older, out-of-warranty unit needs a board and has other faults at the same time.
| Situation | Likely call | Next step |
|---|---|---|
| Gas valve was partly closed | No repair | Reset and monitor |
| Igniter or flame rod dirty or failed | Repair | Service visit plus a small part |
| Gas pressure or gas line problem | Repair the supply, not the heater | Licensed gas pro |
| Board or valve failed, in warranty | Repair | Warranty part, labor covered only in year one |
| Board failed on an older unit with other faults | Price both | Compare with gas tankless installed costs |
The code itself means the burner did not light, so no flame is running. The risk is in what comes next: repeated resets with a gas problem, or opening the cabinet. Smell for gas first and leave internal checks to a pro.
Rheem's chart does not list weather. A blocked outdoor vent or intake falls under the venting check on Rheem's A011 page, so clear the outside terminal and retry.
Rheem's A011 page lists gas pressure and venting first, and both are set during installation. Call the installer back, since the warranty excludes problems from improper installation and gas line sizing.
This guide uses Rheem's US manuals and warranty. Rheem products sold in other countries have their own documents, so check the manual for your model.
Independent Research
Published ranges for tank, tankless and heat pump replacement, the failures that justify a repair, and the ones that do not. Sourced, dated, and free to read.
