Tankless water heaters display error codes when something goes wrong. Understanding what each code means helps you know whether it's a quick reset or something that needs professional repair. This guide covers the most common codes for the major brands we service in Los Angeles.
| Code | Meaning | Common Cause in LA |
|---|---|---|
| Error 3 | Ignition failure | Gas supply issue, dirty igniter |
| Error 10 | Exhaust/intake blockage | Bird nest, debris in vent termination |
| Error 12 | Flame failure during operation | Gas pressure fluctuation, dirty burner |
| Error 27 | Hard water scale alert | LA hard water — annual descaling needed |
| Error 28 | Recirculation flow sensor | Failed pump or sensor in recirculation system |
| Error 36 | Cold water inlet sensor fault | Sensor replacement needed |
| Error 38 | Exhaust sensor | Scale buildup or sensor failure |
| Code | Meaning | Common Cause in LA |
|---|---|---|
| Code 03 | Bath fill timeout | Bath fill function exceeded time limit |
| Code 11 | No ignition | Gas supply, dirty igniter, gas valve |
| Code 12 | Flame failure | Gas pressure, dirty burner assembly |
| Code 14 | Thermal fuse failure | Overheating due to scale — descale first |
| Code 25 | Condensate neutralizer | Routine maintenance — neutralizer replacement |
| Code 31 | Cold water inlet sensor | Sensor failure or wiring issue |
| Code 61 | Combustion fan failure | Fan motor or wiring fault |
| LC | Scale buildup warning | Very common in LA — annual descaling prevents this |
| Code | Meaning | Common Cause in LA |
|---|---|---|
| Code 11 | No ignition | Gas, igniter, PCB |
| Code 12 | Flame failure | Gas valve, burner, sensor |
| Code 16 | Overheating | Scale in heat exchanger — descale needed |
| Code 29 | Condensate neutralizer | Routine maintenance item |
| Code 59 | Scale buildup | Annual descaling prevents in LA hard water |
| Code 90/99 | Combustion abnormality | Venting, gas, or sensor issue |
The #1 cause of tankless water heater error codes in Los Angeles is hard water. LA's water supply — from the LADWP and Metropolitan Water District — has 200–400 mg/L of dissolved minerals, primarily calcium and magnesium.
Over time, these minerals deposit as scale inside the heat exchanger, causing:
Annual descaling prevents most error codes entirely. We recommend all LA homeowners with tankless units schedule annual descaling service. It typically takes 1–2 hours and can add years to the life of your unit.
We diagnose and repair water heater problems throughout the San Fernando Valley and greater LA area.
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