Ruud 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: Ruud's Tankless Water Heater Error Code List names code 12 Flame Failure. The owner causes (gas service interrupted; LP gas running low on LP models) come from the Service Error Code Chart in the RUTG and RUTGH Use and Care manuals linked on Ruud's product pages. Charts differ by series; check your Use and Care manual.

Code 12 on a Ruud tankless gas water heater is "Flame Failure": the burner couldn't keep a flame, so the heater stopped and the water went cold. For homeowners, Ruud's Use and Care manual narrows it to two things: gas service to your home was interrupted, or a propane (LP) model is running low on gas. Get the gas back, reset the heater, and most of the time you're done.

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

What the 12 code means

Ruud's tankless customer support page links a "Common Error Codes" list. On it, code 12 is "Flame Failure."

The Service Error Code Chart in the Use and Care manuals on Ruud's RUTG and RUTGH product pages explains what that usually means in a home:

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

If the gas drops out or runs short, the burner flame fails and the heater locks out with 12. Ruud's list also gives a longer set of technician checks, covered under causes below.

Look-alike codes that mean something different:

• 11: "No Ignition" on Ruud's list. The burner never lit; the manual points to a gas shut-off valve that isn't fully open.
• 10: "Air Supply or Exhaust Blockage" on Ruud's list.
• 14: the manual says the water heater is overheating, and to call a dealer or qualified technician.

Ruud's tankless families (RUTG, RUTGH and older models) don't all use the same chart. Check the one in your own manual.

Likely causes (most common first)

1. Gas service is off or was interrupted. Utility work, a meter change or a service shut-off will do it.
2. The propane tank is low or empty (LP models only).
3. A valve wasn't reopened. After gas work or a tank refill, a valve may still be closed, including the gas shut-off valve on the heater.
4. Air in the gas line. Ruud's list says to bleed all air from the gas lines, which is common after installation or gas work. That's for the installer.
5. Gas type, gas pressure, or undersized piping, meter or regulator. All of these are on Ruud's list for 12, and a licensed gas pro has to check them.
6. Venting, flame rod, gas valves, wiring or grounding. Ruud's list includes all of these too. They're internal or installation checks for a technician.

How to fix it, step by step

Open a hot tap after each step to test. If you smell gas, stop right there and leave.

1. Reset the heater the way Ruud's manual describes. Close all hot taps, turn the heater off at the remote, wait about 5 minutes, turn it on, and open a hot tap.
2. Get your gas service back. If none of your gas appliances work, call the gas utility and let them restore service.
3. Refill or replace the LP container on a propane model. Call your propane supplier and follow their instructions for bringing the system back.
4. Check the gas shut-off valve on the outside of the heater. If it's closed or partly closed, use 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 for any gas to clear. If you smell gas, stop and follow the warning at the top of this page.
   • Turn the valve counterclockwise to ON.
   • Restore power.
5. Power-cycle the heater. Unplug it for about 30 seconds, plug it back in, and test a hot tap.
6. Call your installer after any recent gas work. Air in the line is likely. Don't open fittings to bleed it.
7. Call for service if 12 keeps returning. Ruud's manual says to turn off the tap and heater, write down the code, and call for service.

Test the part

Most of the technician checks on Ruud's list for code 12 (flame rod, gas solenoid valves, wiring harnesses, power supply voltage) happen inside the cabinet with gas and 120-volt power live. None of that is a homeowner test. Ruud's manual warns of a shock hazard behind the cover and says not to attempt repairs to wiring, gas piping, burners or vent connectors. What you can safely do:

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 gas shut-off valve clockwise to OFF.
2. Read the propane tank gauge if you have LP. Leave the tank valve and regulator to your propane supplier.
3. Inspect the gas line from the outside. Look for a kinked or crushed line, but don't tighten or loosen anything.
4. Walk around the vent and air intake outside. Clear snow, leaves or nests you can reach by hand. Ruud's manual calls for 12 inches (30 cm) of clearance at the air intake.
5. Look for signs of fire, flood or impact damage. Ruud's manual says to shut the manual gas valve and have a qualified technician check the heater before using it again.

No meter readings here. The internal flame and valve checks need live gas and power.

When you're finished, 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 when:

• Gas service to the house is off. Restoring it is the utility's job.
• Code 12 returns after gas or propane is back and you've done the reset.
• The heater was just installed, converted or worked on. Bleeding air from the line and confirming gas type belong to the installer.
• You suspect low gas pressure or undersized gas piping, meter or regulator. That takes a gauge and a licensed gas pro.
• Fixing it would mean taking off the cover, or you see scorching, rust or water damage.
• The heater is under warranty. Have the model number, serial number and installation date handy.

Ruud's manual says to take questions and repairs to your installer, plumbing contractor or licensed service agent first. For an existing Ruud tankless heater, Ruud's support page lists 1-866-720-2076, 7 a.m. to 7 p.m. Central, 7 days a week.

FAQ

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