What does Rinnai error code 12 mean?

Code 12 means the flame was lost after ignition, or the heater could no longer confirm it. A part called the flame rod sits in the burner and senses whether a flame is present. If the signal drops out, the control board closes the gas valve as a safety step. Then the heater shows 12.

The difference from code 11 matters. Code 11 is no ignition at all. Code 12 lit, then failed. Because the heater got as far as a flame, gas is usually reaching it, so the search moves to three suspects: how steady the gas pressure is, how well the exhaust and intake air are moving, and how healthy the flame sensing circuit is.

Rinnai's manual leads with gas supply and works inward. The list below follows its order:

• Gas supply or pressure. The gas has to be on at the heater, the meter or the propane tank, and the tank has to have fuel. If pressure sags when the heater ramps up, the flame can lift off the burner. Rinnai says the pressure drop through the gas piping should stay at or under 0.3 inches of water column on natural gas with every gas appliance in the building running. Too small a gas line, or a heater added later to an old line, can break that rule.
• A loose flame rod or electrode. Rinnai says neither the sparker electrode nor the flame rod should move when you push on it with a finger. A loose one, called a floating flame rod, causes code 12 and also code 11.
• Damaged flame rod sleeve or wiring. A cracked silicone sleeve on the flame rod can let the spark go to a ground outside the combustion chamber. Loose or damaged flame rod wiring does the same kind of harm.
• Exhaust recirculation. If the vent joints are not fully seated, or the terminal is too close to a wall or another obstruction, exhaust gases can loop back into the intake. That fouls combustion and drops the flame. Rinnai calls out concentric and common vents that are not fully engaged at each joint.
• Poor grounding or moisture. Rinnai stresses that a properly grounded circuit is critical for flame sensing. Damp wiring can also cause a short that ends in code 12.
• Fan or burner debris. Insects or dirt in the blower wheel, fan housing or burner disturb airflow.
• A regulator problem. Rinnai says a two-stage gas regulator should sit at least six feet from the heater, and that the pressure must not exceed 10 inches of water column on natural gas or 13.5 inches on propane when the heater shuts off.

One special case: on the SENSEI series, Rinnai says a code 12 that shows up immediately when water starts flowing, with no flame visible, points to an electrical short in a component. That one needs a technician with a meter.

Not much is safe to open, but a few checks cost you nothing. First, the gas smell rule, which comes before everything. If you smell rotten eggs, leave, keep switches and openers alone, and call Southwest Gas at 877-860-6020 and 911 from outside. Rinnai's manual gives the same order: no lighting anything, no phones inside, call the gas supplier.

If there is no smell, try this:

1. 1Confirm the gas valve to the heater is fully open and, on propane, that the tank is not low.
2. 2Look at the vent terminal outside. Clear leaves, a nest, or anything stacked against it. Do not touch a hot vent.
3. 3Turn the heater off at its controller, wait a minute, and turn it back on. Run a hot tap for a couple of minutes.
4. 4Note when it started. A code that began right after a storm, a power blip, a gas interruption or new work on the vent tells the technician where to look.

Rinnai's manual also explains how to see the last nine codes from the controller: turn the heater off with the On/Off button, then press and hold On/Off for two seconds together with the Up button. The codes flash one after another. Write them down before you call, because a history of 12, 12, 11, 12 tells a technician more than a single code does. Press and hold the same two buttons to exit, then turn the heater back on.

If code 12 clears and stays away, you are done. If it comes back the same day, stop resetting it. Each cycle repeats the same failed attempt, and the cause needs a real test.

A technician runs down the same list with instruments. They measure inlet gas pressure while the heater fires on high, and confirm it meets the number on the rating plate. They inspect the flame rod, its sleeve and its wiring, and set the electrode gap to 3.5 millimeters, about 0.138 inch. They check the ground circuit and look for moisture. They inspect the fan for debris, verify the vent joints and clearances, and test the gas valve.

Rinnai's manual is direct about who should do this. The steps are for people qualified to service gas systems, and gas system sizing belongs with a professional gas technician or master plumber. Live electrical tests are part of the work too. That is why we say leave the panel closed.

When code 12 keeps coming back, our licensed and insured plumbers can test the gas pressure and flame circuit at any hour, since HQ Plumbing and Air runs 24/7 emergency service. You get a free estimate and the price up front before any work begins.

Some repeat code 12 problems trace to things you can prevent. Keep the vent terminal and the area around the heater clear. Do not store paint, solvents or cleaners near it, since Rinnai warns against flammables near any gas water heater. Have the gas piping checked whenever a new gas appliance is added, because the heater needs its full gas flow even when the range and furnace are running.

Flush the heat exchanger on the schedule Rinnai gives, especially in Phoenix where the water is hard. Scale is not what causes code 12, but a heater that has been left alone for years tends to gather several faults. Our page on descaling a tankless water heater in Phoenix covers timing, and our guide on repairing or replacing a water heater helps if the unit is old.

If you are comparing codes, see our pages on Rinnai error code 11, which is no ignition, and Rinnai error code 10, which is an air supply or exhaust problem. Together those three cover the ignition, flame and air problems that keep a Rinnai from making hot water.

If the display shows LC instead of a number, that is a scale warning, explained on our page on the Rinnai LC code. Owners of other brands can compare with our page on Navien error codes E012 and E016, where E012 is Navien's flame loss code.

Noritz also has a code 12 for flame loss, covered on our page on Noritz error codes 11, 90 and 99.