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Severity: Moderate

Rheem Water Heater Error 11 – Causes & Fix

Rheem tankless didn't light at startup. Rheem's own first fix: check the gas shut-off valve is fully open.

Safety first · Consult a professional

Rheem's manual is explicit that gas piping, burners, controls and vent connectors are not for owner repair. If you smell gas, don't light anything or touch switches, leave the building and call 911 or your gas supplier from outside or a neighbor's phone. If a CO alarm goes off, go outside and call 911.

  • Gas appliance: no DIY repairs. If you smell gas, leave the building, do not use switches and call your gas utility’s emergency line from outside.
  • Carbon monoxide is odorless. Keep a CO alarm near fuel-burning appliances; if it sounds, get everyone outside and call 911.

At a glance

Severity: 3/5 – Moderate3/5

Severity: Moderate

Meaning
Ignition Failure – Gas Not Getting Through
Typical repair cost
$0–$800
DIY difficulty
Hard

On Rheem tankless gas water heaters, code 11 is an ignition failure at startup – the burner didn't light. Rheem's Use & Care manuals list one owner-level cause and fix for it: the gas shut-off valve isn't fully opened, so open it completely. That's a telling hint, because a valve left half-closed after installation or service can pass enough gas for a small appliance but not for a burner rated up to 199,900 Btu/h. Rheem separates this from code 12, which it attributes to interrupted gas service or propane running low while operating. If the valve is fully open and the code survives Rheem's reset sequence, the cause – supply pressure, air in the line, gas-type setup, igniter, flame rod or gas valve – needs a qualified service technician.

How it looks on the display

Rheem Water Heater / Boiler display showing error 11

Model families & display variants

Model familyShowsNote
Condensing and non-condensing RTGH / RTG models with LED remote control11Two-digit code on the remote; the Use & Care chart lists 'gas shut-off valve not fully opened'.
Newer models with LCD user interfaceA011Same fault with an 'A0' prefix; clear it through the SERVICE menu ('Clear Alarms?').
EcoNet app (Wi-Fi models)11App notification mirrors the heater; the gas valve check and reset happen at the unit.

Symptoms

  • No hot water; code 11 on the remote control or user-interface screen
  • Occurs at the start of a draw, not partway through
  • Began right after installation, a water heater service or gas line work
  • Gas shut-off handle sits at an angle rather than fully in line with the pipe
  • Propane homes: tank gauge low or recently run out

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Manual gas shut-off valve not fully open – the cause Rheem's chart names for code 11 28%
  2. Propane tank empty or low, or tank service valve closed 16%
  3. Air in the gas line after installation, service or a propane run-out 14%
  4. Gas line or meter too small, so pressure collapses when the burner tries to light at high input 14%
  5. Igniter or flame rod fouled, cracked or poorly connected 12%
  6. Wrong gas type for the heater, or a conversion not completed 8%
  7. Gas valve or control board failure 8%

Fix it step by step

Diagnostic flow: 111Sniff test first2Open the gas shut-off completely3Check gas availability4Follow Rheem's clearing sequence5Newer LCD models: clear the alarm inthe menu6Call for service with the details

  1. Sniff test first

    If there's any smell of gas near the heater or the piping, don't reset – follow the safety box right away.

  2. Open the gas shut-off completely

    Find the manual valve on the gas line just before the heater. The handle must be fully in line with the pipe; halfway is exactly the situation Rheem's chart describes. Turn it all the way open – never loosen any fittings.

    Tools: Flashlight

  3. Check gas availability

    Confirm the gas range or furnace works. On propane, look at the tank gauge and make sure the tank valve is open; if the tank ran dry, tell your supplier so they can leak-check before restoring service.

  4. Follow Rheem's clearing sequence

    Close all hot taps, switch the heater off at the remote control, wait about 5 minutes and switch it back on. If the code remains, unplug the heater for about 30 seconds, plug it back in and test a hot tap again.

  5. Newer LCD models: clear the alarm in the menu

    Units with the text user interface show A011. Press SERVICE, then ENTER, scroll to 'Clear Alarms?' and confirm 'Yes', then retry a hot tap.

  6. Call for service with the details

    Note the model and serial number from the rating plate and whether you heard clicking at startup. If the code persists, a qualified plumber or gas fitter tests supply pressure and ignition; Rheem's service line is listed in the manual (1-866-720-2076).

How to reset 11

  1. Turn off all hot water faucets.
  2. Turn the heater off with the power button on the remote, wait about 5 minutes, then turn it back on and open a hot tap.
  3. If the code is still there, unplug the heater for about 30 seconds, plug it in and try again (LCD models: SERVICE > ENTER > Clear Alarms? > Yes).
  4. If code 11 persists, turn the heater off, note the code and call for service.

Where the parts are

Boiler: pressure gauge, ignition and flue – 11123456789
Boiler: pressure gauge, ignition and flue
  1. 1Flue
  2. 2Fan
  3. 3Heat exchanger
  4. 4Ignition electrode
  5. 5Gas valve
  6. 6Circulation pump
  7. 7Expansion tank
  8. 8Pressure gauge
  9. 9Temperature sensor

Repair options & costs

RepairDIY?Estimated cost
Open gas shut-off valve fully Yes $0
Propane refill / supplier leak check after run-out No $0–$150
Service call: purge line, measure gas pressure, verify gas type No $130–$260
Replace igniter or flame rod No $170–$360
Replace gas valve or control board No $380–$800

Rough US estimates; technician call-out fees vary by region. Not a quote.

When to call a technician

If the shut-off valve is fully open, other gas appliances work and Rheem's reset sequence doesn't clear code 11, contact your installer or a qualified plumber or gas fitter. Rheem directs all adjustments and repairs to installers or licensed service agents, and anything involving gas pressure, ignition parts or the gas valve belongs there.

Frequently asked questions

Rheem says the gas valve isn't fully open – but it looks open. What now?

Make sure the handle is completely parallel to the pipe and check the meter or tank valve too. If everything upstream is open and the code remains, the gas supply pressure or the ignition system needs testing by a technician.

What's the difference between Rheem code 11 and code 12?

Rheem ties code 11 to the burner not lighting at startup, typically a valve not fully open. Code 12 relates to gas service being interrupted or propane running low, so it tends to show up while the heater is already running.

Why does my new Rheem tankless show A011 instead of 11?

Newer Rheem models with a text display add an 'A0' prefix to the familiar codes. A011 and 11 describe the same ignition problem, and A029 matches code 29.

Does unplugging the heater fix code 11?

The power cycle is part of Rheem's reset routine and clears a one-off lockout. If gas isn't reaching the burner properly, the code simply comes back, and then it's time for service.

Sources