Rinnai Error Code 12

Why a lit burner goes out

The heater keeps the flame going only while a flame rod keeps proving it's there. Lose the gas, lose the air, or lose the signal from the rod, and the controller shuts down to be safe. That's why Rinnai's code 12 checklist is long: it covers gas, venting and the electrical side.

The usual causes

From Rinnai's bulletin and troubleshooting guide, roughly in the order to rule them out:

• Gas not fully on at the heater, the meter or the propane tank, or a propane tank that's nearly empty.
• Gas pressure problems. Rinnai's guide says inlet pressure should never exceed 10 inches of water column on natural gas or 13.5 inches on propane, and it allows only a 0.5-inch pressure drop on propane. An undersized gas line or regulator lets pressure sag once the burner is running.
• Air in the gas lines, usually after a tank refill or gas work.
• A blocked flue or vent, or venting that's too long or built with the wrong materials.
• A dirty or loose flame rod. Rinnai lists carbon buildup on the flame rod and its wiring, and its guide checks that the electrode and flame rod are tight, that the electrode gap is 0.138 inch (3.5 mm), and that the rod's silicone sleeve isn't cracked.
• Grounding, power supply voltage and wiring problems, including moisture in the wiring.
• A propane regulator installed too close to the heater. Rinnai's guide checks that a two-stage regulator sits at least six feet from the water heater.
• Debris or insects in the fan wheel or intake.
• Gas valve, burner or control board faults.

Safe checks you can do

1. Check the propane gauge if you're on propane. A tank at the bottom of its range can light the burner and then fail to keep up. Rinnai's guide starts with making sure the tank has gas in it.
2. Check the gas valve on the line into the heater, and make sure the meter valve is on.
3. Test another gas appliance. If the stove flickers or won't stay lit, the supply is the problem. Call the gas utility or propane supplier.
4. Look at the vent and intake outside. Clear snow, ice, leaves or a nest. Don't reach into the pipe.
5. Think about timing. Does the code show up only when the furnace or dryer runs at the same time? That points toward gas supply or line sizing, and it's worth telling the tech.
6. Reset once. Turn the heater off at the controller, back on, and open a hot tap. If the code returns quickly, stop.

If the code shows up the instant water starts flowing, Rinnai's guide points technicians toward an electrical short. That's not an owner fix.

When to call a technician

Call when the gas supply is solid, the vent is clear and code 12 keeps coming back. Measuring inlet and manifold pressure, cleaning and setting the flame rod, checking grounds and testing the gas valve all happen inside the cabinet.

For budgeting, HomeGuide puts tankless water heater repairs at $300 to $1,300 on average. If the heater is overdue for descaling, a flush on the same visit makes sense; see how to flush a tankless water heater.

Code 12 after a propane refill

If the code shows up right after a refill, especially one after the tank ran empty, think air in the lines. Rinnai lists air in the gas lines as a code 12 cause, and a refill after the tank ran dry is the usual way air gets in. If the code keeps coming back after the lines have been purged, call the propane company to check the regulator and pressure.

For the rest of the codes, see our Rinnai tankless error codes guide.