What do Rinnai tankless error codes mean? Full code table

Before you use this table

If you smell gas, do not reset anything. Leave on foot, avoid anything that can spark, and call the gas utility and 911 from a safe place^[2].

The table below paraphrases Rinnai's diagnostic code guide in our own words^[1]. It is not Rinnai's text. Rinnai splits its line into SENSEI condensing models (RX, CX, RE, RSC, sold since 2019), non-SENSEI models (V-series, RL, RU, RUR, RUC and commercial C-series), and the RH180 hybrid. The "Applies to" notes tell you which. Meanings marked with an asterisk (*) are inferred from the checks Rinnai lists for that code; confirm them in your model's manual.

"Power cycle once" means turning the unit off and back on one time. If the code returns, stop.

Rinnai code table

Code	What it means	Safe homeowner check	Call a pro when
02*	Freeze protection ran but the burner could not fire (non-SENSEI)	Gas valve to the heater open; gas service on	Code returns with gas confirmed on
03*	Power was lost mid-cycle, such as during a bath fill	Close hot taps, press On/Off twice, retry	It keeps coming back (possible board fault)
05	Bypass flow control valve fault	Power cycle once	It returns: the valve needs testing or replacement
07*	RH180 only: low water supply pressure, pump not running, or clogged filter	Cold supply valve open; clean the inlet filter	Pump or heat exchanger service is needed
10	Combustion air or exhaust blocked, or a full condensate trap (condensing)	Clear snow, leaves or nests from the outside vent; check the condensate line drains	It returns: vent system or heat exchanger needs inspection
11	No ignition: burner did not light	Gas valve open at the heater and meter; propane tank not empty; power cycle once	Still no light: gas pressure, igniter or flame rod check
12	Flame lit, then went out	Confirm gas supply; note if it fails when other gas appliances run	Any repeat: gas pressure test under load, flame rod, venting
13*	Poor combustion on B-vent (atmospheric) models	Note whether opening the door to the room helps, and tell the pro	Always: venting or combustion air needs correcting
14	Overheat protection tripped. Rinnai says to take this one seriously	Shut the unit off; do not keep resetting	Always
15*	SENSEI: gas valve or venturi control fault	Power cycle once; check vent terminals are clear	It returns
16	Outlet water hotter than expected	Check the vent terminal and the space around the unit for obstructions	It returns, especially with a recirculation system
17*	SENSEI: venturi or vent blockage; unit locks out	Check the condensate line and vent terminals	Always: the venturi must be cleaned and the lockout reset
19*	Electrical grounding or current leakage fault	Power cycle only	Always: electrical diagnosis
21*	SENSEI: board data transfer fault, usually after a board replacement	None	Always: the board needs reprogramming
25	Condensate backup (condensing models)	Check the condensate line for kinks, clogs or ice	Trap or neutralizer service is needed
30 or FE	RH180: flammable vapor sensor tripped	Leave the area until it is safe; then remove gasoline, paint or solvents from the room	Sensor testing, or if you smell gas
31*	RH180: burner manifold gas pressure setting problem	None	Always: gas pressure adjustment
32, 33, 34, 35, 38, 41, 51*	A temperature sensor reads out of range: outlet water (32), heat exchanger outlet (33), combustion air (34), RH180 tank (35), exhaust (38), outdoor or freeze protection (41), inlet water (51)	Power cycle only	Always: sensor test and replacement
52	Modulating gas valve signal fault	None	Always
54	Exhaust temperature too high (Rinnai cites about 163 F)	Check the vent terminal	Heat exchanger service or vent repair is needed
57, 58	Non-SENSEI condensing (KB): a safety switch opened on the burner (57) or secondary heat exchanger (58)	None	Always: usually overheating or blockage
61	Combustion fan fault	None	Always: fan or wiring
63*	Recirculation problem: pump, settings, or air in the loop	None	Always: recirculation setup or pump service
65	Water flow control (servo) valve fault	None	Always
70, 71, 72, 73*	Internal control faults: board parameters (70), gas solenoid circuit (71), flame sensing (72), burner sensor (73, non-SENSEI)	Power cycle once	Always if it returns
79	Internal water leak detected (non-SENSEI)	Shut off water and power to the unit; put a pan under it	Always
FF	Not a fault: a marker that maintenance was done	No action	n/a
SE	SENSEI commercial cascade message	None	Cascade wiring or setup issue
SS	SENSEI: service reminder; a heat exchanger flush is due	Schedule a flush; the owner's manual gives the reset steps	You prefer not to flush it yourself
LC (LC0 to LC9)	Scale building up in the heat exchanger (non-SENSEI). The unit keeps running	Schedule a flush; consider water treatment	Before it progresses to a shutdown code

Source: Rinnai document 100000652^[1], paraphrased.

The codes owners see most

10, 11 and 12 account for many no-hot-water calls, and all three start with things you can check: the outside vent, the gas valve and the gas supply. If you are on propane, check the tank first.

14 is the one not to fight. An overheat trip means something let the unit get too hot. Shut it off and call.

LC and SS are maintenance prompts. Ignoring them lets scale build until it causes overheat or flow faults, which are more expensive. A flush and descale typically runs $75 to $300, per HomeGuide's 2025 figures^[3].

When to call a pro

• Code 14, or any code tied to a sensor, gas valve, fan or board.
• Codes 10, 11 or 12 that return after the checks above.
• Code 79, or any water visible inside or under the cabinet.
• An RH180 flammable vapor code (30 or FE) if the cause is not obvious.