Ruud Ultra Series tankless units (RU130, RU160, RU180, RU199) use the same numeric error code system as Rheem RTGH tankless — same manufacturing, same firmware. Codes are 2-digit numeric and display on the digital controller.
The top codes you\'ll actually see
| Code | Meaning | Most common cause |
|---|---|---|
| 11 | Ignition failure | Gas supply / igniter / flame sensor |
| 12 | Flame failure during operation | Dirty flame sensor / vent |
| 14 | Overheat / heat exchanger | Scaled heat exchanger |
| 79 | Combustion fan motor | Fan motor / RPM sensor |
| 99 | Exhaust restriction | Vent blockage / icing |
Full numeric reference
| Code | Description |
|---|---|
| 11 | Ignition failure / no flame |
| 12 | Flame failure during operation |
| 13 | Combustion abnormality |
| 14 | Heat exchanger overheat |
| 15 | Boiling sensor |
| 16 | Outlet thermistor |
| 21 | Inlet thermistor |
| 25 | Condensate drain blocked |
| 29 | Combustion abnormality (secondary) |
| 32 | Outlet sensor |
| 33 | Heat exchanger thermistor |
| 52 | Modulating gas valve |
| 61 | Combustion fan motor |
| 65 | Water flow control valve |
| 70 | Control board (PCB) |
| 72 | Flame sensing circuit |
| 76 | Communication fault (remote controller) |
| 79 | Combustion fan |
| 80 | Internal communication |
| 90 | Combustion abnormality (general) |
| 99 | Exhaust blockage / vent restriction |
| LC | Low water flow |
Tank gas units — LED indicator
Ruud tank gas units (Classic, Achiever, Achiever Plus, Ultra, Power Vent) use a status LED on the gas valve — same system as Rheem and similar to AO Smith\'s LED flash codes. Watch the LED flash pattern to identify the fault.
Electric units — no LED code system
Electric tanks diagnose via: breaker check → ECO red button reset → multimeter test of upper element/thermostat → lower element/thermostat.
Professional Hybrid — alphanumeric display
Hybrid units have a digital display with mode and alphanumeric codes:
- P1 / P2 — temperature sensor
- F1 / F2 — control board
- HP — heat pump compressor lockout
- EL — resistance backup element
How to reset
- Tankless: press On/Off button on controller; if persists, power cycle at breaker for 30 seconds
- Gas tank: cycle gas knob (off → pilot → on)
- Electric tank: red ECO button on upper thermostat
- Hybrid: mode button → ECO reset → breaker cycle
Bottom line
For tankless, each code has a specific cause — click linked codes above for diagnostic walkthroughs. For tank units, LED indicator on gas valve. For electric, multimeter testing.