Rinnai tankless water heater code 13: Combustion fault
Tankless water heater, United States
The heater detected a combustion problem. The checks cover venting, combustion air, altitude settings and gas pressure.
This needs a licensed gas or HVAC technician. There are a few safe checks you can do first, marked below. Anything inside the unit is a job for a professional.
This involves the flue or exhaust. A blocked or leaking flue can let carbon monoxide into the home.
Only some models show this code. Check the list below.
What causes it
-
Vent materials or joints not installed to the manufacturer's requirements, or vent clearance problems.
Check the outside flue or vent terminal is clearYou can do this
- Find where the flue or vent pipe ends outside the building. High-efficiency furnaces and some water heaters also have a combustion air intake pipe beside it: check that one too. On some outdoor water heaters the flue outlet is part of the front cover.
- Look for anything blocking it, such as leaves, a bird or insect nest, snow, plants, or items stored against the wall.
- Cut back plants and move stored items away from it. Do not touch, poke into or hose the flue outlet. If something is inside it, book a service. The terminal can be hot. Do not climb onto the roof or use a ladder to reach it; if it is out of reach, book a technician.
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Not enough combustion air in the room for all the gas appliances installed there.
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Altitude dip switches set wrong, or inlet or manifold gas pressure out of range.
How to read this code on your unit
Booking a licensed gas or HVAC technician
Book a licensed gas or HVAC technicianlicensed gas or HVAC technician
- Turn the unit off and leave the covers on. Gas components must only be serviced by a licensed technician.
- Note the code, how often it appears, and the model and serial numbers from the rating label.
- Book a licensed gas or HVAC technician and give them those details.
Models that show this code
32 models in 7 ranges
| Range | Models |
|---|---|
| Commercial (KB) | C199i (REU-KBD3237FFUDC-US), C199e (REU-KB3237WDC-US) |
| KB | RU80i (REU-KB2530FFUD-US), RU80e (REU-KB2530WD-US), RU90e (REU-KBD2934WD-US), RU98i (REU-KB3237FFUD-US), RU98e (REU-KB3237WD-US) |
| KBD | RUC80i (REU-KBD2530FFUD-US), RUC90i (REU-KBD2934FFUD-US), RUC98i (REU-KBD3237FFUD-US) |
| KBP | RUR98i (REU-KBP3237FFUD-US), RUR98e (REU-KBP3237WD-US) |
| KCM | RUCS65i (REU-KCM2025FFU-US), RUCS75i (REU-KCM2528FFU-US), RUS65e (REU-KCM2025W-US), RUS75e (REU-KCM2528W-US) |
| Luxury (VC) | 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) |
| Value (VC) | 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) |
Where this comes from
- Troubleshooting tankless water heater diagnostic codes (100000652), non-SENSEI and SENSEI series , page 20
Checked against the manufacturer's manual on 9 October 2026.
Other Rinnai tankless water heater codes
| Code | Meaning | What you can do |
|---|---|---|
| 02 | Burner did not light during freeze protection | Safe checks first, then a pro |
| 03 | Power cut during bath fill | You can often fix it |
| 05 | Bypass flow control failure | Safe checks first, then a pro |
| 10 | Air intake, flue or condensate blockage | Safe checks first, then a pro |
| 11 | No ignition | Safe checks first, then a pro |
| 12 | Flame failure or low gas flow | Safe checks first, then a pro |
| 14 | Overheat safety device tripped | Call a pro |
| 15 | Venturi control failure | Safe checks first, then a pro |
| 16 | Over-temperature shutdown | Safe checks first, then a pro |
| 17 | Venturi blockage | Safe checks first, then a pro |
| 18 | Gas valve adjustment limit | Call a pro |
| 19 | Electrical earth fault | Call a pro |
See all flue or venting fault codes on tankless water heaters across brands.