Identify your tankless water heater series
Error codes are published per series, not per brand. Before you look up a number, you need to know which series you own — and that comes off the model number, not the badge on the front.
Step 1 — find the model number
Every unit carries a rating label printed with its model number. It is the same number the manufacturer's own support line will ask you for. Look on the casing — front panel, side, or underneath near the connections — for a label with the model, the serial number and the gas type.
If the unit is boxed in or mounted high, the model number is also on the installation paperwork, the original invoice, and often on a sticker inside the front cover.
Reading a label is all this needs. Do not remove panels, open the casing, or disconnect anything to find it — and if you smell gas, leave the area and call your gas utility from outside.
Step 2 — match it to a series
Find your model number below. The series it belongs to is the code table you should be reading.
Rinnai
| If your model number is… | Your series | Codes |
|---|---|---|
| C199i (REU-KBD3237FFUDC-US), C199e (REU-KB3237WDC-US), RC80i (REU-KA2530FFUD-US), RC80e (REU-KA2530WD-US), RC98i (REU-KA3237FFUD-US), RC98e (REU-KA3237WD-US), RU80i (REU-KB2530FFUD-US), RU80e (REU-KB2530WD-US), RU90e (REU-KBD2934WD-US), RU98i (REU-KB3237FFUD-US), RU98e (REU-KB3237WD-US), RUC80i (REU-KBD2530FFUD-US), RUC90i (REU-KBD2934FFUD-US), RUC98i (REU-KBD3237FFUD-US), RUR98i (REU-KBP3237FFUD-US), RUR98e (REU-KBP3237WD-US), RUCS65i (REU-KCM2025FFU-US), RUCS75i (REU-KCM2528FFU-US), RUS65e (REU-KCM2025W-US), RUS75e (REU-KCM2528W-US), RE140i (REU-VE1720FFD-US), RE140e (REU-VE1720WD-US), RE160i (REU-VE2125FFD-US), RE160e (REU-VE2125WD-US), RE180i (REU-VE2432FFD-US), RE180e (REU-VE2432WD-US), RE199i (REU-VE2737FFD-US), RE199e (REU-VE2737WD-US), REP160i (REU-VEP2125FFD-US), REP160e (REU-VEP2125WD-US), REP199i (REU-VEP2730FFD-US), REP199e (REU-VEP2730WD-US), R50LSi (REU-VA2019FFUD), R63LSe2 (REU-VA2024WD(A)-UC), R75LSi (REU-VA2528FFUD(A)), R75LSe (REU-VA2528WD(A)-UC), R94LSi (REU-VA2535FFUD), R94LSe (REU-VA2535WD-UC), R98LSi (REU-VA3237FFU), R98LSe (REU-VA3237W-US), R98LSi-ASME (REU-VA3237FFU-ASME), R98LSe-ASME (REU-VA3237W-ASME), RL75i (REU-VB2528FFUD-US), RL75e (REU-VB2528WD-US), RL94i (REU-VB2735FFUD-US), RL94e (REU-VB2735WD-US), V53e (REU-VAM1620W-US), V53De (REU-AM1620WD-US), V65i (REU-VC2025FFU-US), V65e (REU-VC2025W-US), V75i (REU-VC2528FFU-US), V75e (REU-VC2528W-US), V94i (REU-VC2837FFU-US), V94Xi (REU-VC2737FFU-US), V94e (REU-VC2837W-US), RL75i (REU-VC2528FFUD-US), RL75i(A) (REU-VC2528FFUD-US(A)), RL75e (REU-VC2528WD-US), RL75e(A) (REU-VC2528WD-US(A)), RL94i (REU-VC2837FFUD-US), RLX94i (REU-VC2737FFUD-US), RL94e (REU-VC2837WD-US) | Non-SENSEI | 31 |
| RH180, REU-VA1320WF-US | RH180 Hybrid | 20 |
| RU199i / RU199e (REU-N3237FF-US / REU-N3237W-US), RU180i / RU180e (REU-N2934FF-US / REU-N2934W-US), RU160i / RU160e (REU-N2530FF-US / REU-N2530W-US), RU130i / RU130e (REU-N2024FF-US / REU-N2024W-US), RUR199i / RUR199e (REU-NP3237FF-US / REU-NP3237W-US), RUR160i / RUR160e (REU-NP2530FF-US / REU-NP2530W-US), RSC199i / RSC199e (REU-NP3237FF-US(A) / REU-NP3237W-US(A)), RSC160i / RSC160e (REU-NP2530FF-US(A) / REU-NP2530W-US(A)) | SENSEI | 27 |
| RX199i (REU-NB3237FF-US), RX180i (REU-NB2934FF-US), RX160i (REU-NB2530FF-US), RX130i (REU-NB2024FF-US), RXP199i (REU-NBP3237FF-US), RXP160i (REU-NBP2530FF-US) | SENSEI RX | 31 |
Navien
| If your model number is… | Your series | Codes |
|---|---|---|
| NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 | NPE-2 | 32 |
| NPE-180A, NPE-210A, NPE-240A, NPE-150S, NPE-180S, NPE-210S, NPE-240S | NPE-A / NPE-S | 27 |
Rheem
| If your model number is… | Your series | Codes |
|---|---|---|
| Not published by the manufacturer — see the note below | Tankless Gas | 33 |
Tankless Gas: Rheem's own service pocket manual (SVC820) covers its gas tankless range as a single code table, marking which codes apply only to high-efficiency (condensing) units and which only to indoor installations. It does not enumerate model numbers, so neither do we — what matters for reading these codes is whether your unit is condensing (it has a condensate drain line and an acid neutralizer) and whether it is installed indoors. Codes 29A, 92 and 93 are condensing-only; codes 05 and 13 are indoor-only.
Noritz
| If your model number is… | Your series | Codes |
|---|---|---|
| EZ98DV (EZTR50), EZ111DV (EZTR75), NCC199CDV, GQ-C2859WX-FF US, GQ-C3259WX-FF US, GQ-C3259WZ-FF US | EZ Series & NCC199CDV | 26 |
| NCC199-SV, NCC199-DV, N-0841MC-DV, NRC111-SV, NRC111-DV, N-0842MC-DV | NCC199 & NRC111 | 25 |
| NR50-OD, NR66-SV, NR66-OD, N-0531S-OD, NR71-SV, NR71-OD, N-0631S-OD | NR50, NR66 & NR71 | 17 |
| NR98-SV, NR98-OD, NR98-DVC, NC199-OD, NC199-DVC, N-0751M-OD, N-0751M-DV, N-0751M-DVC, NR111-SV, NR111-OD, NR111-DV, NC250-SV-ASME, NC250-DV-ASME, N-0931M-OD, N-0931M-DV, NC380-SV-ASME, N-1321M-ASME | NR98 & NR111 | 25 |
| NRC661-DV, NRC661-OD, NRC711-DV, NRC711-OD, NRC663-FSV (EZTR40), NR501-OD, NR662-OD | NRC Series | 25 |
| NRCP111-DV, NRCP98-DV | NRCP | 28 |
| NRCP1112-DV, NRCP982-DV | NRCP Eco TOUGH | 28 |
Takagi
| If your model number is… | Your series | Codes |
|---|---|---|
| Not published by the manufacturer — see the note below | Condensing | 24 |
| T-D2, T-K4, T-KJr2 | Non-Condensing | 18 |
Condensing: Takagi publishes a separate troubleshooting guide for its condensing on-demand models, and the codes below are that guide's table. Two of them are worth knowing before you need them: 101 is a warning for abnormal combustion and 991 is the error it becomes, and 711 covers a hi-limit switch that has a physical reset button — Takagi's own first step on several other codes is to check whether that button has tripped. The non-condensing range has its own guide and its own table.
Why this step is not optional
The clearest example on this site is Rinnai code 34. On a SENSEI RX it is the lime detecting thermistor clamped to the hot water pipe. On Rinnai's older non-SENSEI units the same number is the combustion air temperature thermistor in the fan housing — a different part, in a different place, with a resistance range around five times higher, and Rinnai routes the two to different verdicts. Someone working from a brand-level answer buys the wrong sensor.
Once you know your series, go straight to the full code table and find your number under it.