Rinnai Water Heater Error Codes

Look up what a blink or error code means on your Rinnai water heater, and whether it is safe to check yourself.

This is a gas appliance. If you smell gas or hear hissing, leave the house and call your gas utility or 911 from outside. Repairs to gas lines or burners are a job for a licensed technician.

This table covers Rinnai tankless water heaters, both the older Non-SENSEI line and the newer SENSEI line. The RH180 hybrid tank-tankless model is not covered here.

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Rinnai Non-SENSEI Series tankless (on-demand) gas water heaters, including V, VA, VB, VC, KA, KB, KBD, KBP, KCM, RC, RE, and RL model lines (2-digit and letter diagnostic codes shown on the temperature controller)

Code	Severity	What it means	Safe checks
02	Safety hazard	In cold weather the heater tries to run its burner briefly to keep itself from freezing, but the burner did not fire correctly.	2 safe checks Check that other gas appliances in the home are working, to confirm the gas supply is on Look at the breaker panel to see if the water heater's breaker has tripped
03	DIY OK	The heater's power was briefly interrupted while it was running or filling a bath, so it stopped and shows this code. Only if the code clears after turning the water heater off and back on with the ON/OFF button on the controller, per the manual. If the code comes back after trying this a few times, call a professional to replace the control board.	1 safe check Look at the breaker panel to see if the water heater's breaker has tripped
05	Pro required	A valve that controls a small bypass of water inside the heater is not working the way it should.	None needed
10	Safety hazard	The heater is not getting enough fresh air, its exhaust vent is blocked, or its condensate drain is full, so it shut off to protect itself.	2 safe checks Look at the vent cap outside to see if it is blocked by snow, leaves, or debris Look at the condensate drain line where it leaves the building to see if it is visibly frozen or clogged
11	Safety hazard	The heater tried to light its burner but could not get a flame started, usually because of a gas, spark, or venting problem.	2 safe checks Check that other gas appliances in the home are working, to confirm the gas supply is on Look at the breaker panel to see if the water heater's breaker has tripped
12	Safety hazard	The burner's flame went out or never lit properly, so the heater shut itself off for safety.	1 safe check Check that other gas appliances in the home are working, to confirm the gas supply is on
14	Safety hazard	A safety switch tripped because part of the heater got too hot, so it shut down to protect itself.	1 safe check Look at the vent outside to make sure it has proper clearance and is not blocked
16	Safety hazard	The water leaving the heater got hotter than it is supposed to, so the heater is warning you about it.	1 safe check Look at the temperature setting on the control panel to see if it was set unusually high
19	Pro required	The heater found a problem with its electrical grounding connection.	None needed
25	Pro required	The pump that drains condensate water is not working, or its drain line is clogged or frozen.	1 safe check Look at the condensate drain line to see if it is visibly frozen or blocked where it exits the building
31	Safety hazard	A sensor that checks the burner's flame temperature is giving a reading that is outside the normal range.	None needed
32	Pro required	The sensor that checks the temperature of the water leaving the heater is not working correctly.	None needed
33	Pro required	A temperature sensor on the heat exchanger is not working correctly.	None needed
34	Pro required	The sensor that checks the temperature of the combustion air is not working correctly.	None needed
38	Pro required	The sensor that checks the exhaust gas temperature is not working correctly.	None needed
41	Pro required	The outdoor sensor that helps protect the heater from freezing is not working correctly.	None needed
51	Pro required	The sensor that checks the temperature of the water coming into the heater is not working correctly.	None needed
52	Safety hazard	The main gas valve is not working the way it should.	1 safe check Check that other gas appliances in the home are working, to confirm the gas supply is on
54	Safety hazard	The exhaust gas got too hot, so the heater lowered its power and then shut down to protect itself.	1 safe check Look at the vent termination outside for proper clearance and any blockage
57	Safety hazard	A safety switch on the burner tripped because it got too hot, so the heater shut down.	1 safe check Check that other gas appliances in the home are working, to confirm the gas supply is on
58	Safety hazard	A safety switch on the secondary heat exchanger tripped because it got too hot, so the heater shut down.	None needed
61	Safety hazard	The fan motor that supplies air for the burner is not working correctly.	None needed
63	Pro required	Water is not flowing fast enough through the recirculation system.	1 safe check Clean the external cold water inlet filter, if your model has one, by shutting the isolation valves and rinsing the filter screen, per the owner's manual
65	Pro required	The valve that controls water flow inside the heater is not working correctly.	None needed
70	Pro required	The heater's main control board has a fault and likely needs to be replaced.	None needed
71	Safety hazard	The gas solenoid valve that turns gas flow on and off is not working correctly.	1 safe check Check that other gas appliances in the home are working, to confirm the gas supply is on
72	Safety hazard	The flame rod, which senses whether the burner is lit, has a fault.	None needed
73	Safety hazard	The sensor that checks the burner's flame temperature has a fault.	None needed
79	Pro required	The heater detected water leaking inside its cabinet.	1 safe check Look around the base of the water heater for any standing water or visible leaks
FF	Normal	This is not an error. It is a note in the heater's history showing that a technician performed maintenance or service.	None needed
00, LC, LC0-LC9	Pro required	The heat exchanger has scale buildup from hard water and needs to be flushed before damage occurs.	None needed

Sources

Rinnai Troubleshooting Tankless Water Heater Diagnostic Codes (official technical bulletin, doc 100000652, current edition covering Non-SENSEI, SENSEI, and SENSEI RX/CX Series) (accessed 2026-07-03)
Rinnai Troubleshooting Tankless Water Heater Diagnostic Codes (earlier edition of doc 100000652, used to cross-check that shared codes did not change meaning) (accessed 2026-07-03)
Rinnai Tankless Water Heater Installation and Operation Manual (N Series Residential Condensing), Care and Maintenance / Filters section (accessed 2026-07-03)
Fix Rinnai Error Codes (11, 12, LC & More): An Easy DIY Guide, tanklesshotwaterguide.com (used only for cross-checking common code meanings, not as a primary source) (accessed 2026-07-03)
Rinnai Error Codes, hotwaternowco.com (used only for cross-checking common code meanings, not as a primary source) (accessed 2026-07-03)

Rinnai SENSEI Series and SENSEI RX/CX Series tankless (on-demand) gas water heaters, including RU, RUR, RSC, CU, RX, RXP, and CX model lines (2-digit and letter diagnostic codes shown on the temperature controller and in the Rinnai app)

Code	Severity	What it means	Safe checks
03	DIY OK	The heater's power was briefly interrupted while it was running or filling a bath, so it stopped and shows this code. Only if the code clears after turning the water heater off and back on with the ON/OFF button on the controller, per the manual. If the code comes back after trying this a few times, call a professional to replace the control board.	1 safe check Look at the breaker panel to see if the water heater's breaker has tripped
05	Pro required	A valve that controls a small bypass of water inside the heater is not working the way it should.	None needed
10	Safety hazard	The heater is not getting enough fresh air, its exhaust vent is blocked, or its condensate drain is full, so it shut off to protect itself.	2 safe checks Look at the vent cap outside to see if it is blocked by snow, leaves, or debris Look at the condensate drain line where it leaves the building to see if it is visibly frozen or clogged
11	Safety hazard	The heater tried to light its burner but could not get a flame started, usually because of a gas, spark, or venting problem.	2 safe checks Check that other gas appliances in the home are working, to confirm the gas supply is on Look at the breaker panel to see if the water heater's breaker has tripped
12	Safety hazard	The burner's flame went out or never lit properly, so the heater shut itself off for safety.	1 safe check Check that other gas appliances in the home are working, to confirm the gas supply is on
14	Safety hazard	A safety switch tripped because part of the heater got too hot, so it shut down to protect itself.	1 safe check Look at the vent outside to make sure it has proper clearance and is not blocked
15	Safety hazard	The part that mixes air and gas for the burner, called the venturi, is not being controlled correctly.	None needed
16	Safety hazard	The water leaving the heater got hotter than it is supposed to, so the heater is warning you about it.	1 safe check Look at the temperature setting on the control panel to see if it was set unusually high
17	Safety hazard	The part that mixes air and gas for the burner, called the venturi, is blocked and cannot work properly.	None needed
18	Safety hazard	The smart gas valve reached the limit of how much it can adjust the air and gas mixture.	1 safe check Check that other gas appliances in the home are working, to confirm the gas supply and gas type are correct
19	Pro required	The heater found a problem with its electrical grounding connection.	None needed
21	Pro required	The control board did not receive its setup information correctly, often after a new board was installed.	None needed
22	Safety hazard	The smart gas valve's position switch is not lined up the way it should be.	None needed
25	Pro required	The pump that drains condensate water is not working, or its drain line is clogged or frozen.	1 safe check Look at the condensate drain line to see if it is visibly frozen or blocked where it exits the building
32	Pro required	The sensor that checks the temperature of the water leaving the heater is not working correctly.	None needed
33	Pro required	A temperature sensor on the heat exchanger is not working correctly.	None needed
34	Pro required	The sensor that checks the temperature of the combustion air is not working correctly.	None needed
38	Pro required	The sensor that checks the exhaust gas temperature is not working correctly.	None needed
41	Pro required	The outdoor sensor that helps protect the heater from freezing is not working correctly.	None needed
51	Pro required	The sensor that checks the temperature of the water coming into the heater is not working correctly.	None needed
52	Safety hazard	The main gas valve is not working the way it should.	1 safe check Check that other gas appliances in the home are working, to confirm the gas supply is on
54	Safety hazard	The exhaust gas got too hot, so the heater lowered its power and then shut down to protect itself.	1 safe check Look at the vent termination outside for proper clearance and any blockage
61	Safety hazard	The fan motor that supplies air for the burner is not working correctly.	None needed
63	Pro required	Water is not flowing fast enough through the recirculation system.	1 safe check Clean the external cold water inlet filter, if your model has one, by shutting the isolation valves and rinsing the filter screen, per the owner's manual
65	Pro required	The valve that controls water flow inside the heater is not working correctly.	None needed
66	Pro required	A valve that controls a small bypass of water inside the heater is not working correctly.	1 safe check Clean the external cold water inlet filter, if your model has one, by shutting the isolation valves and rinsing the filter screen, per the owner's manual
70	Pro required	The heater's main control board has a fault and likely needs to be replaced.	None needed
71	Safety hazard	The gas solenoid valve that turns gas flow on and off is not working correctly.	1 safe check Check that other gas appliances in the home are working, to confirm the gas supply is on
72	Safety hazard	The flame rod, which senses whether the burner is lit, has a fault.	None needed
FF	Normal	This is not an error. It is a note in the heater's history showing that a technician performed maintenance or service.	None needed
SE	Normal	This is shown on the main heater in a multi-unit commercial system to say that one of the other connected heaters has an error. Check the display on that other unit to find its specific code.	1 safe check Look at the display on the other connected water heater units to find which one is showing the actual error code
SS (55)	Normal	This is a reminder, not a breakdown. It means it is time to have the heat exchanger flushed as regular maintenance.	None needed
00, LC, LC0-LC9	Pro required	The heat exchanger has scale buildup from hard water and needs to be flushed before damage occurs.	None needed

Sources

Rinnai Troubleshooting Tankless Water Heater Diagnostic Codes (official technical bulletin, doc 100000652, current edition covering Non-SENSEI, SENSEI, and SENSEI RX/CX Series) (accessed 2026-07-03)
Rinnai Tankless Water Heater Installation and Operation Manual (N Series Residential Condensing), Care and Maintenance / Filters section (accessed 2026-07-03)
Rinnai Error Codes, hotwaternowco.com (used only for cross-checking common code meanings, not as a primary source) (accessed 2026-07-03)

Last updated 2026-07-03.