Rinnai tankless water heaters show a numeric error code when they shut down. The code tells you exactly what the unit objected to. Below are the codes we see most often in San Diego, what each one actually means, and what fixes it. If your unit is showing a code right now, call Drain Masters at (619) 346-4212.
Rinnai Code 10 — Air Supply or Exhaust Blockage
Code 10 means the unit is not getting the air it needs or cannot vent properly. Check for a blocked or crushed vent, debris or a bird nest in the termination, a vent run that is too long, or a collapsed intake. Clear the obstruction and confirm the vent is sealed and correctly sized.
Rinnai Code 11 — No Ignition
The burner is not lighting. Confirm the gas is on, the propane tank is not empty, and other gas appliances work. If gas is present, the igniter or flame rod is usually the culprit and needs service.
Rinnai Code 12 — Flame Failure
The unit lit but lost flame. Common causes are low gas pressure, an undersized gas line, a dirty flame rod, or air in the line. Gas pressure should be checked with a manometer.
Rinnai Code 14 — Thermal Fuse / Overheat
A safety cutoff tripped from overheating, usually caused by heavy scale build-up inside the heat exchanger. San Diego hard water makes this common. Descaling is the fix; a damaged exchanger needs replacement.
Rinnai Code 16 — Overheat Warning
The outlet temperature exceeded the safe limit. Scale, restricted flow, or a failing thermistor are the usual causes. Flush the unit and verify flow rate.
Rinnai Code 25 — Condensate Drain Blocked
On condensing units, the condensate line is clogged or improperly trapped. Clear the line and confirm it drains freely.
Rinnai Code 29 — Condensate Drain / Heat Exchanger
Blocked condensate drain on the secondary heat exchanger. Clear the drain and check the trap.
Rinnai Code 79 — Combustion Fault
The unit is not burning cleanly, usually a gas-pressure or venting problem. This one should be diagnosed by a licensed plumber, not reset repeatedly.
Rinnai Code LC / LC0 — Scale Build-Up Warning
Not a failure yet — a warning that scale is accumulating. Descale now and you avoid Code 14 later. In hard-water San Diego we recommend descaling roughly once a year.
Frequently Asked Questions
Can I reset a Rinnai error code myself?
You can clear a code by turning the unit off and back on, but a code that returns is telling you something real. Repeatedly resetting a Code 14 or 79 without fixing the cause risks damaging the heat exchanger.
Why do Rinnai units in San Diego scale up so fast?
San Diego water is hard. Mineral scale coats the inside of the heat exchanger, insulates it, and drives the overheat codes (14, 16, LC). Annual descaling is the single best preventive step.
How much does it cost to fix a Rinnai error code?
It depends entirely on the code. A descale or condensate-line clearing is routine; an ignition, gas-pressure or heat-exchanger fault costs more. We quote before we start.
Is it worth repairing or should I replace the unit?
If the heat exchanger is sound, most codes are repairable and worth fixing. If the exchanger has failed from long-term scale, replacement is usually the better spend.
Read the deep dive on Error Code 10, or see our tankless water heater service in San Diego. Call (619) 346-4212.