Noritz tankless water heaters display two-character numeric error codes on the controller. Codes are consistent across NRC, EZTR, EZ, NRCB combi, and NCC commercial lines (some legacy units use 3-character codes prefixed with "C" — same meaning). The codes below cover the current Noritz controller generation.
The top codes you'll actually see
| Code | Meaning | Most common cause |
|---|---|---|
| Code 11 | No ignition | Gas supply / igniter / flame rod |
| Code 12 | Flame failure during operation | Dirty flame rod / vent restriction |
| Code 14 | Overheat / heat exchanger | Scaled heat exchanger |
| Code 29 | Combustion fan | Fan motor / blockage |
| Code 90 | Combustion abnormality | Vent / gas pressure |
| Code 99 | Exhaust restriction | Vent blockage / icing |
Full numeric reference
| Code | Description |
|---|---|
| 05 | Bypass servo error |
| 10 | Combustion air supply restricted |
| 11 | Ignition failure / no flame |
| 12 | Flame failure during operation |
| 14 | Overheat — thermal fuse trip |
| 16 | Outlet thermistor fault |
| 20 | Tank/inlet thermistor |
| 21 | Inlet thermistor |
| 22 | Outlet thermistor |
| 23 | DHW thermistor (combi) |
| 25 | Condensate drain blocked |
| 29 | Combustion fan fault |
| 31 | Burner sensor |
| 32 | Heat exchanger thermistor |
| 33 | Outdoor sensor (combi) |
| 52 | Modulating gas valve solenoid |
| 61 | Combustion fan motor |
| 65 | Flow control valve |
| 70 | Control board (PCB) |
| 71 | Solenoid valve circuit |
| 72 | Flame sensing circuit |
| 76 | Cascade communication / Quick Connect cord |
| 79 | Combustion fan |
| 80 | Internal communication |
| 90 | Combustion abnormality |
| 99 | Exhaust blockage / vent restriction |
| LCO | Low water flow — insufficient GPM to activate |
| HCO | High water flow — outside operating range |
| 101 | Exhaust temperature |
| 111 | Drain valve / installer alert |
How to reset
Three reset levels:
- Level 1 — controller reset: press the On/Off button for 3 seconds
- Level 2 — power cycle: turn off at the breaker, wait 30 seconds, restore. Clears all running state
- Level 3 — service menu: requires Noritz installer password. Don't attempt without installer guidance
If the code returns within 60 seconds of reset, the underlying fault is active. Don't keep cycling — work through the specific code's diagnostic walkthrough.
Bottom line
Each code on the page list above has a specific cause and diagnostic sequence. Click the linked codes for the detailed walkthrough. For cases without a displayed code, see general troubleshooting.