A code on a Rinnai tankless display means one of the unit's built-in safety checks failed, not a general malfunction light. Rinnai's own troubleshooting manual, document 100000652, lists dozens of numbered codes covering ignition, flame loss, blocked venting, overheating, condensate backup, water flow and scale, and most of them apply across its current SENSEI-tier models and its older Non-SENSEI models.
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Rinnai's manual groups its lineup as SENSEI Series (the RU and RUR series) and older Non-SENSEI models (its V, VC, KB and KCM series), with the RL series documented separately. Rinnai's residential tankless page uses the SE+ name for the current SENSEI condensing tier: the RX, RXP, RUS and RUCS models.
The table below groups codes by what they report, since a code number alone means less than the fault family it belongs to.
| Fault family | Example codes | What it is reporting |
|---|---|---|
| Ignition | 11 | No spark, or gas did not light on a call for hot water |
| Flame | 12 | A flame lit, then dropped, or a wiring short is mimicking that pattern |
| Airflow or venting | 10, 16 | The vent or air intake is restricted, or the unit is overheating because of it |
| Condensate | 25 | Condensate backed up and tripped a safety switch, or the condensate pump stopped |
| Water flow | 65 | The water flow control valve did not close during a bath-fill cycle |
| Scale | LC, 00, 58 | Mineral build-up inside the heat exchanger is cutting heat transfer |
| Sensor or control board | 31, 32, 33, 70 to 73 | A sensor, wiring harness or the control board itself has failed |
Source: Rinnai, Technical Bulletin 75, Condensing Water Heater Error Codes, August 2010, and Rinnai, Troubleshooting Tankless Water Heater Diagnostic Codes, document 100000652, accessed August 2026.
Code 11 means the unit tried to ignite and never got a flame. Code 12 means it did get a flame and then lost it, or has a wiring short somewhere in its ignition circuit. Rinnai's technical bulletin lists both under the same troubleshooting path, which starts at the gas supply and ends at parts only a licensed technician can test.
One check is genuinely safe for a homeowner: confirm the gas valve is open at the water heater and at the meter, or that a propane tank has not run dry. Rinnai's bulletin lists that as the first step for code 11. The full code 11 checklist, split by model group with Rinnai's page numbers, is in Rinnai tankless water heater code 11.
Code 12 is less homeowner-friendly. If it appears as soon as water flow starts, Rinnai's manual attributes that to an electrical short in a component rather than a gas problem, isolated by a technician one component at a time. How a technician traces that short, and the vent faults behind a delayed code 12, are covered in Rinnai code 12 flame failure.
| Code | Fault | First step in Rinnai's bulletin | Homeowner-safe? |
|---|---|---|---|
| 11 | No ignition | Confirm gas is on at the water heater, meter or propane cylinder | Yes, that one check |
| 12 | Flame failure | Confirm gas is on, then check for vent obstructions and wiring | Mostly no, needs the case opened |
Source: Rinnai, Technical Bulletin 75, Condensing Water Heater Error Codes, August 2010.
Code 10 is an air supply or exhaust blockage: the unit cannot draw combustion air in or push exhaust out through its vent. Code 16 is an over-temperature warning, tied to the same restricted airflow, a circulating system on low flow, or a heat exchanger clogged enough to trap heat.
The one homeowner-safe check for either code is outside the house: confirm the vent terminal is not blocked by snow, leaves, a bird's nest, or another vent blowing into it. Rinnai's bulletin lists that as its first step for code 10. Past that, both codes involve gas pressure, dip-switch settings and fan inspection, treated as technician work in the same bulletin.
| Code | Fault | Homeowner check | Deeper cause |
|---|---|---|---|
| 10 | Air supply or exhaust blockage | Vent terminal clear outside | Vent length, dip switches, fan blockage |
| 16 | Over-temperature warning | None reliably safe | Low circulating flow, clogged exchanger |
Source: Rinnai, Technical Bulletin 75, Condensing Water Heater Error Codes, August 2010.
The full checklist, with vent-length math and warranty exclusions, is in the Rinnai tankless water heater code 10 guide.
Code 25 means the condensate safety switch has tripped, and that only happens when condensate backs up inside the unit or an external condensate pump stops moving it out. It is specific to Rinnai's condensing models, since a non-condensing unit produces no condensate to drain in the first place.
Two checks are within reach for most homeowners: look at the condensate drain line for a kink, a freeze point or a blockage, and confirm any external condensate pump has power. Rinnai's manual lists both as the first two steps for this code, before it moves to wiring and the trap itself.
| What to check | What it points at |
|---|---|
| Condensate line kinked, frozen or blocked | Most likely cause, per Rinnai's manual |
| External condensate pump has no power | Second listed cause |
| Neither found | Trap or float switch itself, technician territory |
Source: Rinnai, Troubleshooting Tankless Water Heater Diagnostic Codes, document 100000652, accessed August 2026.
Code 65 means the water flow control valve failed to close during a bath-fill cycle, and it is the one code on Rinnai's list paired with a direct action rather than just a diagnosis. Rinnai's own bulletin says to shut off the water and stop the bath-fill function right away, then contact a state-qualified or licensed contractor to service the unit.
That instruction exists because a valve stuck open during a fill cycle can keep filling past where it should stop. Rinnai does not attach this kind of direct action instruction to any other code on its list.
| Code | Fault | Rinnai's instruction |
|---|---|---|
| 65 | Water flow control valve failed to close during bath fill | Shut off the water, stop the bath-fill function, then call a state-qualified or licensed contractor |
Source: Rinnai, Technical Bulletin 75, Condensing Water Heater Error Codes, August 2010.
Code 61 is a combustion fan motor fault; Rinnai's step-by-step checks and costs are in our Rinnai code 61 guide.
LC, 00 and LC0 through LC9 all report scale build-up inside the heat exchanger, and it is the only code on Rinnai's list that lets the unit keep running while it is displayed. The display alternates between the code and the set temperature, and the controller keeps beeping until the exchanger is flushed.
Rinnai's bulletin describes a temporary reset: pressing the on/off button five times buys about 70 hours before the code returns, and each unflushed use advances the count, so LC2 means three resets without a flush. It buys time to schedule service, not a fix. Rinnai documents this for Non-SENSEI models; a related code, 58, covers scale on the secondary heat exchanger of that group.
| Code | Meaning | Temporary workaround | Actual fix |
|---|---|---|---|
| LC, 00, LC0 to LC9 | Scale in the primary heat exchanger | Press on/off 5 times for about 70 hours | Flush the heat exchanger |
| 58 | Scale on the secondary heat exchanger, bi-metal switch tripped | None documented | Flush, then a hard power reset |
Source: Rinnai, Technical Bulletin 75, August 2010, and Rinnai, Troubleshooting Tankless Water Heater Diagnostic Codes, document 100000652, accessed August 2026.
A normal display with no hot water often means the unit never got a signal to fire, so no code appears. Rinnai's manual points first at a clogged inlet filter, a flow rate below the minimum activation threshold, or hot and cold lines crossed at installation.
Cleaning the inlet filter is one check a homeowner can do without opening anything electrical or gas-related. Rinnai's manual also lists causes behind a related complaint, a cold water sandwich, a burst of cold water arriving between two draws of hot water:
For symptom-by-symptom coverage that applies across brands and to storage tank units, see the general water heater problems page.
Source: Rinnai, Troubleshooting Tankless Water Heater Diagnostic Codes, document 100000652, accessed August 2026.
Leak detection: see what Rinnai code 79 means and why condensation can trigger it.
A short list is genuinely safe to check without training: whether the gas valve is open, whether the vent terminal outside is clear, whether the condensate line is frozen or blocked, and whether the inlet water filter is clean. Past that, opening the case, testing voltage or replacing a sensor is technician work.
Rinnai's manual is explicit that adjusting the internal gas valve voids the warranty, since it is not meant to need field adjustment. It is equally direct about a gas smell: do not light the water heater, do not touch an electrical switch, and call the gas supplier from outside the building, or the fire department if the supplier cannot be reached.
For what Rinnai's warranty covers and how to find an authorized servicer, see the Rinnai water heater repair guide. For symptoms and cost ranges across brands and tank units, see the water heater problems page, and for equipment pricing by series, see the Rinnai tankless water heater cost guide.
Source: Rinnai, Troubleshooting Tankless Water Heater Diagnostic Codes, document 100000652, accessed August 2026.
Every code and instruction on this page is listed here with its Rinnai source document and date. If a detail is not traceable to this list, it should not be treated as sourced.
Codes can change between manual revisions. Confirm the code on your display against your own owner's manual before treating a table here as final.
No ignition: the unit tried to fire but never got a flame. Rinnai's Technical Bulletin 75 lists checking that gas is on at the water heater, the meter or the propane cylinder as the first step, and that check is safe for a homeowner to make.
The water flow control valve failed to close during a bath-fill cycle. Rinnai's bulletin pairs this code with a direct instruction: shut off the water, stop the bath-fill function, and contact a state-qualified or licensed contractor.
Scale build-up inside the heat exchanger. It is the only code that lets the unit keep operating while displayed, and pressing the on/off button five times buys about 70 hours before it returns. The fix is flushing the heat exchanger, per Rinnai's Technical Bulletin 75.
For a handful of codes, the first step is homeowner-level: confirming the gas valve is open, clearing the vent terminal, checking the condensate line, or cleaning the inlet filter. Past that, Rinnai's manual moves into voltage tests and parts a technician has to open the unit to reach.
Rinnai's manual points first at a clogged inlet filter, a flow rate below the unit's minimum activation threshold, or hot and cold lines crossed at installation, all of which keep the unit from starting a heating cycle, so no code has a reason to appear.
Mostly. Rinnai's manual lists most fault codes, including ignition, flame, airflow and condensate faults, as applying to both its current SENSEI-tier models and its older Non-SENSEI models. The LC scale code and code 58 are documented specifically for Non-SENSEI models.
Independent Research
Published ranges for tank and tankless replacement, the failures that justify a repair, and the ones that do not. Sourced, dated, and free to read.
