HVACopediaRinnai tankless water heater error codes
45 codes with causes and test steps, plus 13 settings tables.
| Code | Meaning | Severity |
|---|---|---|
| 02 | Burner did not operate during freeze protection | High |
| 03 | Power interrupted during bath fill | Low |
| 05 | Bypass flow control device fault | Medium |
| 07 | Circulation flow rate below 2.1 GPM | Medium |
| 10 | Air supply or exhaust blocked / condensate trap full | Critical |
| 11 | No ignition | High |
| 12 | Flame failure | High |
| 13 | Combustion fault | Critical |
| 14 | Thermal fuse or overheat sensor tripped | Critical |
| 15 | Venturi control fault | High |
| 16 | Outlet water over-temperature safety shutdown | Critical |
| 17 | Venturi blockage | High |
| 18 | Gas valve air/fuel adjustment limit reached | High |
| 19 | Electrical grounding / DC circuit short | High |
| 21 | PC board data transfer error | High |
| 22 | Gas valve adjustment fault | Medium |
| 25 | Condensate pump failure or clogged drain | Medium |
| 30 | Flammable vapor sensor activated or faulty | Critical |
| 31 | Burner thermocouple out of range | High |
| 32 | Outlet water temperature thermistor fault | Medium |
| 33 | Heat exchanger thermistor fault | Medium |
| 34 | Combustion air thermistor (Non-SENSEI) / Lime detecting thermistor (RX/CX) | Medium |
| 35 | Tank temperature sensor fault | Medium |
| 38 | Exhaust gas temperature sensor (CO sensor on RH180) | Critical |
| 41 | Freeze protection / outdoor air temperature sensor fault | Medium |
| 51 | Inlet water temperature thermistor fault | Medium |
| 52 | Gas valve / modulating solenoid valve (POV) signal fault | High |
| 54 | High exhaust gas temperature | Critical |
| 57 | Burner overheat bi-metal switch open | Critical |
| 58 | Secondary heat exchanger bi-metal switch open | High |
| 61 | Combustion fan motor fault | High |
| 63 | Recirculation low flow | Medium |
| 65 | Water flow control device (servo) fault | Medium |
| 66 | Bypass flow servo fault | Medium |
| 70 | PC board fault | High |
| 71 | Gas solenoid valve fault (SV0–SV4 on Non-SENSEI) | High |
| 72 | Flame rod fault | High |
| 73 | Burner thermocouple fault | High |
| 79 | Water leakage detected | High |
| FE | Flammable vapors detected | Critical |
| FF | Maintenance performed (history marker) | Low |
| LC | Scale build-up in heat exchanger (LC, LC0–LC9, 00) | Medium |
| SE | Cascade diagnostic display (error on secondary unit) | Medium |
| SEt | Initial settings not yet confirmed | Low |
| SS | Service Soon alert (also listed as 55) | Low |
Settings and specs
RSC supply connection sizes
Specifications · SENSEI
| Connection | Size |
|---|---|
| Gas | 3/4 in. NPT |
| Cold inlet | 3/4 in. NPT |
| Hot outlet | 3/4 in. NPT |
| Condensate drain | 1/2 in. NPT |
| Pressure relief valve | M33 thread |
- The PRV and its adapter come in the box; PRV must be rated 150 psi and at least the heater Btu/h.
- Condensate drain line must stay at least 1/2 in. over its whole length.
Source: Rinnai RSC SENSEI Installation and Operation Manual (100000773), Table 3 Supply Connections, p.14
RSC water quality limits
Water quality · SENSEI
| Contaminant | Maximum level |
|---|---|
| Total hardness | Up to 200 mg/L |
| Aluminum | Up to 0.2 mg/L |
| Chlorides | Up to 250 mg/L |
| Copper | Up to 1.0 mg/L |
| Dissolved CO2 | Up to 15.0 mg/L |
| Iron | Up to 0.3 mg/L |
| Manganese | Up to 0.05 mg/L |
| pH | 6.5 to 8.5 |
| TDS | Up to 500 mg/L |
| Zinc | Up to 5 mg/L |
- Damage from water above these limits is not covered by warranty.
- Hard water should be treated; use the Service Soon (SS) reminder (parameter 03) for flushing intervals.
Source: Rinnai RSC SENSEI Installation and Operation Manual (100000773), Table 5 Water Quality Guidelines, p.19
RSC clearances to combustibles
Clearances · SENSEI
| Location | Clearance |
|---|---|
| Top | 2 in. (51 mm); 0 in. from vent components |
| Bottom/ground | 12 in. (305 mm) |
| Front | 0 in.; 24 in. (610 mm) service clearance |
| Back | 0 in. |
| Sides | 2 in. (51 mm); add 0.25 in. (6.35 mm) for recess box |
| Vent | 0 in. |
| Front exhaust (outdoor models) | 24 in. (610 mm) |
- Same values apply to combustible and non-combustible surfaces.
Source: Rinnai RSC SENSEI Installation and Operation Manual (100000773), Table 6 Clearances, p.22
RSC temperature settings available
Installer menu / Control settings · SENSEI
| F | C | Note |
|---|---|---|
| 98 | 37 | - |
| 100 | 38 | - |
| 102 | 39 | - |
| 104 | 40 | Default after power loss if unit was powered under 6 h |
| 106 | 41 | - |
| 108 | 42 | - |
| 110 | 43 | Highest setting while hot water is flowing |
| 115 | 46 | - |
| 120 | 49 | Default max; crossover mode minimum |
| 125 | 52 | Needs parameter 01b |
| 130 | 54 | Needs parameter 01b |
| 135 | 57 | Needs parameter 01b |
| 140 | 60 | Needs parameter 01b |
- While hot water is running the setting can only be changed between 98 F and 110 F.
- Switch F/C: hold On/Off 5 s with the heater off.
- Above 125 F (52 C) water can scald; check local code limits for public buildings.
Source: Rinnai RSC SENSEI Installation and Operation Manual (100000773), Table 32, p.69-70
RX supply connection sizes
Specifications · SENSEI RX/CX
| Connection | Size |
|---|---|
| Gas | 3/4 in. MNPT |
| Cold inlet | 3/4 in. MNPT |
| Hot outlet | 3/4 in. MNPT |
| Condensate drain | 1/2 in. MNPT |
- Vent connection: 2 in. nominal PVC/CPVC/PP or 3 in./5 in. concentric.
- Full specs (input, flow, weight) are only on each model's spec sheet, not in this manual.
- Supplied power cord is 6.5 ft (2.0 m), outdoor rated; 120 VAC 60 Hz grounded.
Source: Rinnai SENSEI RX Residential Installation and Operation Manual (100000839(03)), Table 2 Supply Connections, p.8; power p.45
RX water quality limits
Water quality · SENSEI RX/CX
| Contaminant | Maximum level |
|---|---|
| Total hardness | Up to 200 mg/L |
| Aluminum | Up to 0.2 mg/L |
| Chlorides | Up to 250 mg/L |
| Copper | Up to 1.0 mg/L |
| Dissolved CO2 | Up to 15.0 mg/L |
| Iron | Up to 0.3 mg/L |
| Manganese | Up to 0.05 mg/L |
| pH | 6.5 to 8.5 |
| TDS | Up to 500 mg/L |
| Zinc | Up to 5 mg/L |
- Water damage beyond these limits is not covered by warranty.
Source: Rinnai SENSEI RX Residential Installation and Operation Manual (100000839(03)), Table 4 Water Quality Guidelines, p.11
RX water treatment and flushing by hardness
Water quality · SENSEI RX/CX
| Class | Hardness mg/L | Grains/gal | Treatment | Flushing |
|---|---|---|---|---|
| Soft | 0-60 | 0-4 | None | None |
| Slightly hard | 61-120 | 4-7 | Softener or Rinnai Scale Cutter recommended | Residential once/year; commercial twice/year |
| Moderately hard | 121-160 | 7-9 | Softener or Rinnai Scale Cutter recommended | Residential once/year; commercial twice/year |
| Very hard | 161-200 | 9-12 | Softener or Rinnai Scale Cutter strongly recommended | Residential once/year; commercial twice/year |
| Extremely hard | 200+ | 12+ | Softener or Rinnai Scale Cutter required | Residential once/year; commercial twice/year |
- Use parameter 03 (Service Soon) to remind the owner to flush.
Source: Rinnai SENSEI RX Residential Installation and Operation Manual (100000839(03)), Table 3 Recommended Water Treatment, p.11
RX clearances to combustibles
Clearances · SENSEI RX/CX
| Location | Clearance |
|---|---|
| Top | 2 in. (51 mm); 0 in. from vent components |
| Bottom/ground | 12 in. (305 mm) |
| Front | 0 in.; 24 in. (610 mm) service clearance |
| Back | 0 in. |
| Sides | 2 in. (51 mm); add 0.25 in. (6.35 mm) for recess box |
| Vent | 0 in. |
- Same values for combustible and non-combustible surfaces.
- Freeze protection down to -22 F (-30 C) indoors and -4 F (-20 C) outdoors with power on and no direct wind (p.12).
Source: Rinnai SENSEI RX Residential Installation and Operation Manual (100000839(03)), Table 5 Clearances, p.13
RX temperature settings available
Installer menu / Control settings · SENSEI RX/CX
| F | C | Note |
|---|---|---|
| 98 | 37 | - |
| 100 | 38 | - |
| 102 | 39 | - |
| 104 | 40 | Default after power loss if unit was powered under 6 h |
| 106 | 41 | - |
| 108 | 42 | - |
| 110 | 43 | Highest setting while hot water is flowing |
| 115 | 46 | - |
| 120 | 49 | Default max; crossover mode minimum |
| 125 | 52 | Needs parameter 01b |
| 130 | 54 | Needs parameter 01b |
| 135 | 57 | Needs parameter 01b |
| 140 | 60 | Needs parameter 01b |
- While hot water is running the setting can only be changed between 98 F and 110 F (37-43 C).
- Switch F/C: hold On/Off 5 s with the heater off. Outdoor units auto-lock the controller after 30 min idle.
Source: Rinnai SENSEI RX Residential Installation and Operation Manual (100000839(03)), Table 29 Temperature Settings, p.57-58
RUCS/RUS unit clearances
Clearances · Non-SENSEI
| Location | RUCS indoor to combustibles | RUCS indoor to non-combustibles | RUS outdoor to combustibles | RUS outdoor to non-combustibles |
|---|---|---|---|---|
| Top | 6 in. (152 mm) * | 2 in. (51 mm) * | 12 in. (305 mm) | 2 in. (51 mm) |
| Back | 0 in. | 0 in. | 0 in. | 0 in. |
| Front | 6 in. (152 mm) | 6 in. (152 mm) | - | - |
| Front (panel) | - | - | 24 in. (610 mm) | 0 in. |
| Front (exhaust) | - | - | 24 in. (610 mm) | 24 in. (610 mm) |
| Sides | 2 in. (51 mm) | 1/2 in. (13 mm) | 6 in. (152 mm) | 1/8 in. (3.2 mm) |
| Ground/bottom | 12 in. (305 mm) | 12 in. (305 mm) | 12 in. (305 mm) | 2 in. (51 mm) |
| Vent | 0 in. | 0 in. | - | - |
- 0 in. from vent components and condensate drain line.
- Service clearance 24 in. in front of the heater; closet installs need 6 in. (152 mm) in front.
- RUCS models are indoor only and RUS models are outdoor only.
Source: Rinnai KCM Series (RUCS/RUS) Installation and Operation Manual (U328-0700X04(00)), Unit clearances, p.10
RUCS/RUS water quality limits
Water quality · Non-SENSEI
| Contaminant | Maximum level |
|---|---|
| Total hardness | Up to 200 mg / L |
| Aluminum | Up to 0.2 mg / L |
| Chlorides | Up to 250 mg / L |
| Copper | Up to 1.0 mg / L |
| Dissolved CO2 | Up to 15.0 mg / L or PPM |
| Iron | Up to 0.3 mg / L |
| Manganese | Up to 0.05 mg / L |
| pH | 6.5 to 8.5 |
| TDS | Up to 500 mg / L |
| Zinc | Up to 5 mg / L |
- Scale build-up shows as code LC# on a controller (LC on the status monitor without one); flush the heat exchanger.
- ScaleCutter parts: 103000038 (system), 103000039 (refill).
Source: Rinnai KCM Series (RUCS/RUS) Installation and Operation Manual (U328-0700X04(00)), Water Quality, p.6
Water quality limits - RU/RUR/CU
Water quality · SENSEI
| Contaminant | Maximum level |
|---|---|
| Total hardness | Up to 200 mg/L |
| Aluminum | Up to 0.2 mg/L |
| Chlorides | Up to 250 mg/L |
| Copper | Up to 1.0 mg/L |
| Dissolved carbon dioxide (CO2) | Up to 15.0 mg/L |
| Iron | Up to 0.3 mg/L |
| Manganese | Up to 0.05 mg/L |
| pH | 6.5 to 8.5 |
| TDS (total dissolved solids) | Up to 500 mg/L |
| Zinc | Up to 5 mg/L |
- Damage from water beyond these levels is not covered by warranty.
- Hard water needs treatment and more frequent flushing; the Service Soon (SS) reminder can be enabled.
Source: Rinnai Tankless Water Heater (Residential) Installation and Operation Manual (100000467) Table 5 p.19; Rinnai Tankless Water Heater (With Pump) Installation and Operation Manual (100000508) Table 5 p.19; Rinnai Tankless Water Heater (Commercial) Installation and Operation Manual (100000504) Table 5 p.19
Clearances - RU/RUR/CU
Clearances · SENSEI
| Location | Clearance to combustibles and non-combustibles |
|---|---|
| Top | 2 in. (51 mm); 0 in. from vent components |
| Bottom / ground | 12 in. (305 mm) |
| Front | 0 in.; 24 in. (610 mm) in front for servicing |
| Back | 0 in. |
| Sides (left and right) | 2 in. (51 mm); add 0.25 in. (6.35 mm) for recess box |
| Vent (indoor models) | 0 in. |
| Front exhaust (outdoor models) | 24 in. (610 mm) |
Source: Rinnai Tankless Water Heater (Residential) Installation and Operation Manual (100000467) Table 6 p.22; Rinnai Tankless Water Heater (With Pump) Installation and Operation Manual (100000508) Table 6 p.22; Rinnai Tankless Water Heater (Commercial) Installation and Operation Manual (100000504) Table 6 p.22
Models covered
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.