Rheem Water Heater Code 12: What It Means and How to Fix It

By Dan Mercer · Published October 5, 2026 · Updated October 6, 2026 · Codes covered: 12 · Sources

Verify in your manual: The owner meaning (gas service interrupted, or LP gas running low on LP models) is from the Service Error Code Chart in Rheem's tankless Use and Care manuals (RTGH condensing and RTG non-condensing). The Flame Failure name comes from the error code list on the support page of Ruud, Rheem's sister brand. Codes vary by series; check your Use and Care manual.

Code 12 on a Rheem tankless gas water heater means the heater isn't getting the gas it needs to keep the burner going. Rheem's owner chart gives two causes: your gas service has been interrupted, or, on propane (LP) models, the LP gas is running low. Both are usually fixed outside the heater, by your gas utility or propane supplier, and then a simple reset.

This 3-minute fix saved 0 homeowners a technician visit this month.

What the 12 code means

The Service Error Code Chart in Rheem's tankless Use and Care manuals lists two causes for code 12:

• "Gas service has been interrupted." Rheem's fix: "Contact your gas utility company."
• "LP gas is running low (LP models only)." Rheem's fix: "Refill or replace your LP gas container."

Rheem tankless heaters have no standing pilot. When the gas supply drops out or runs short, the burner flame can't keep going, so the heater shuts down and shows 12.

Ruud, Rheem's sister brand, publishes a tankless error code list that calls code 12 "Flame Failure." Technician literature goes deeper into flame-loss diagnostics, but you don't need it for the owner checks on this page.

Look-alike codes that mean something different:

• Code 11: the burner never lit. Rheem's chart points to a gas shut-off valve that isn't fully open.
• Code 14: the water heater is overheating. Rheem says to contact a dealer or qualified technician.
• Code 29: the neutralizer is clogged (condensing models).

Rheem's tankless lines don't all share one chart. Check the "Service Error Code Chart" in your own Use and Care manual.

Likely causes (most common first)

1. Gas service interrupted. The utility shut off gas for work in the area, the meter was changed, or service was cut off.
2. Propane tank low or empty on LP models.
3. A gas valve not reopened after work or a refill, including the heater's own gas shut-off valve.
4. Air in the gas line after gas work or a tank swap. Ruud's list for code 12 says to bleed all air from the gas lines. That's an installer's job.
5. Gas pressure, gas type, or undersized gas piping. Ruud's list includes these, along with the meter and regulator size. A licensed gas pro has to check them.
6. Venting or internal parts. Ruud's list also covers venting, the flame rod, gas valves, grounding and wiring. These all need a technician.

How to fix it, step by step

Try a hot tap after each step. If you smell gas at any point, stop and get out.

1. Do Rheem's reset. Close all hot taps, turn the heater off at the remote, wait about 5 minutes, turn it back on, and open a hot tap.
2. Confirm you have gas service. If no gas appliance works, call your gas utility. Let them restore service and relight what they need to.
3. Refill or replace the LP container on propane models. Call your propane supplier and follow their instructions to restore service.
4. Make sure the heater's gas shut-off valve is fully open. It's on the outside of the unit. If it was closed, follow the Operating Instructions label on the heater:
   • Turn off all electric power to the heater.
   • Turn the gas shut-off valve clockwise to OFF.
   • Wait 5 minutes to clear out any gas. If you smell gas, stop and follow the gas warning at the top of this page.
   • Turn the valve counterclockwise to ON.
   • Turn the power back on.
5. Power-cycle the heater. Unplug it for about 30 seconds, plug it back in, and try a hot tap.
6. Think about what just changed. A new install, gas work, a meter swap or a propane delivery can leave air in the line. Call your installer or gas supplier. Don't loosen fittings to bleed it yourself.
7. Call for service if 12 keeps coming back. Rheem's manual says to turn off the tap and heater, note the code, and call for service.

Test the part

Code 12 is a gas supply problem first. The parts a technician might check inside (flame rod, gas valves, burner) sit behind the front cover, next to live gas and 120-volt wiring. That isn't homeowner work. Here's what you can check safely:

1. Unplug the water heater and turn off the gas. Pull the plug (or switch off the breaker on hard-wired outdoor models), then turn the heater's gas shut-off valve clockwise to OFF.
2. Look at the propane tank gauge on LP models. Don't adjust the tank valve or regulator. Your propane supplier handles that.
3. Look over the gas line from the outside only. Check for a kinked or crushed line. Don't tighten or loosen anything.
4. Check the vent and air intake outdoors. Clear snow, leaves or nests you can reach by hand. Rheem says the air intake needs 12 inches (30 cm) of clearance.
5. Look for damage. Rheem says to turn off the manual gas shut-off valve if the heater has been through overheating, fire, flood or physical damage. Don't use it until a qualified technician checks it.

Leave the cover on. There are no meter readings to give here, because the internal checks need live gas and power.

When you're done, follow the Operating Instructions label to turn the gas back on and restore power.

Safety notes

When to call a pro

Call your gas utility, propane supplier, or a licensed plumber or gas technician if:

• Your gas service is off. The utility restores it, not you.
• Code 12 comes back after gas service or propane is restored and you've reset the heater.
• The heater is new, was converted, or gas work was just done. Bleeding air from the line and checking gas type are installer jobs.
• You suspect low gas pressure or undersized gas piping. Checking that takes a gauge and a licensed gas pro.
• The heater is under warranty. Have the model number, serial number and installation date ready.

Rheem's manual says to start with your installer, plumbing contractor or licensed service agent. Rheem's contact page lists water heating support at (800) 432-8373, Monday to Friday, 7 a.m. to 7 p.m. Central.

FAQ

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