Rheem Water Heater Error Codes

Look up what a blink or error code means on your Rheem 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 the RTG series and digital display tankless models. A separate Professional series, Classic series, or storage tank code table was not found.

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Rheem RTG series tankless gas water heaters, second generation, up to 199,000 BTU (models RTG2-42, RTG-53, RTG-66, RTG-74; indoor, outdoor, and direct vent). This same numeric two-digit code format is shared with Paloma-built units sold under the Rheem and Ruud brands.

Code	Severity	What it means	Safe checks
00	Pro required	The burner ran without stopping for a full hour, which trips a built in safety timer. This is only seen on first generation units made before July 2006.	1 safe check Look to see if a hot water recirculation pump is installed and running non stop, since constant pump use is a common cause on these older units
03	Pro required	The control board lost communication with an optional MIC 180 or EZ Link accessory module. This code only appears on units with that accessory installed.	None needed
05	Safety hazard	The water heater detected a combustion air problem, which can happen when the air supply to the burner or the exhaust venting is restricted.	2 safe checks Look at the outdoor vent and air intake openings for visible blockage such as leaves, snow, or nests Check that nothing is stacked or stored close to the unit that could block its air openings
10	Safety hazard	The unit is warning that its air supply or exhaust vent may be partly blocked. The manual notes this is a warning signal, not a full shutdown fault.	1 safe check Look at the vent pipe connections and the outdoor vent termination for visible blockage or disconnection
11	Safety hazard	The water heater tried to light the burner but never got a flame, so it shut itself down for safety.	2 safe checks Look at other gas appliances in the home, such as the stove or furnace, to see if they are working, which shows whether the home has gas supply Visually check the breaker panel to see if the water heater's breaker has tripped
12	Safety hazard	The burner lit successfully but then the flame went out during operation, so the unit shut down.	2 safe checks Look at other gas appliances in the home to see if they are working, which shows whether the home has gas supply Visually check the breaker panel to see if the water heater's breaker has tripped
13	Safety hazard	A sensor that watches for poor air quality around the unit detected a problem and shut off the burner as a precaution.	1 safe check Look to see if the space around the unit has been closed in or if boxes or items are blocking fresh air openings nearby
14	Safety hazard	A safety device sensed the unit was overheating and shut off the burner.	1 safe check Look for anything blocking airflow around the unit or blocking the outdoor vent
15	Safety hazard	A safety device sensed the water inside the unit was close to boiling and shut off the burner to prevent damage.	1 safe check Look at the cold water inlet valve to see if it appears fully open
16	Safety hazard	The unit sensed the water temperature climbing too high and issued a warning before it would shut down.	1 safe check Look for anything blocking airflow around the unit or blocking the outdoor vent
21	Pro required	A switch that checks whether the air filter access door is closed is not sensing it as closed, so the unit will not run. This applies to indoor models only.	1 safe check Look at the air filter access door and front panel to see if they appear fully closed and seated
24	Pro required	A switch used to turn the unit on and off is not working correctly.	None needed
29	Pro required	The water coming out of the heat exchanger is cooler than expected, often linked to restricted airflow.	1 safe check Look at the air inlet screen on the outside of the unit for visible blockage such as leaves or debris
31	Pro required	The sensor that measures incoming cold water temperature is not working correctly.	None needed
32	Pro required	The sensor that measures the heat exchanger temperature is not working correctly.	None needed
33	Pro required	The sensor that measures the outgoing hot water temperature is not working correctly.	None needed
34	Pro required	The sensor that measures the combustion air temperature is not working correctly.	1 safe check Look for anything blocking airflow around the unit or the outdoor vent terminal
35	Pro required	One of the unit's temperature sensors is not connected the right way inside the unit.	None needed
38	Safety hazard	The sensor that checks for safe combustion air quality is not responding to its own self test.	1 safe check Look to see if there is enough open space and ventilation around the unit
51	Safety hazard	A valve that controls incoming gas to the burner is not working correctly.	2 safe checks Look at other gas appliances in the home to see if they are working, which shows whether the home has gas supply Visually check the breaker panel to see if the water heater's breaker has tripped
52	Safety hazard	A valve that adjusts the gas flow to control heat output is not working correctly.	2 safe checks Look at other gas appliances in the home to see if they are working, which shows whether the home has gas supply Visually check the breaker panel to see if the water heater's breaker has tripped
61	Safety hazard	The combustion fan that pulls air through the unit is not working correctly.	1 safe check Visually check the breaker panel to see if the water heater's breaker has tripped
65	Pro required	The valve that controls water flow through the unit is not working correctly.	1 safe check Visually check the breaker panel to see if the water heater's breaker has tripped
66	Pro required	The valve that controls water bypass through the unit is not working correctly.	1 safe check Visually check the breaker panel to see if the water heater's breaker has tripped
71	Safety hazard	A gas inlet valve is not responding correctly to the control board's commands.	2 safe checks Look at other gas appliances in the home to see if they are working, which shows whether the home has gas supply Visually check the breaker panel to see if the water heater's breaker has tripped
72	Safety hazard	The part that senses whether a flame is present is not working correctly.	1 safe check Visually check the breaker panel to see if the water heater's breaker has tripped
76	Pro required	The control board lost communication with the wall mounted remote control.	1 safe check Look at the remote control cable for any visible damage, fraying, or disconnection
79	Safety hazard	The combustion fan motor is drawing an incorrect amount of electrical current.	1 safe check Visually check the breaker panel to see if the water heater's breaker has tripped
80	Safety hazard	The unit failed to fully shut off its gas supply the way it is supposed to.	2 safe checks Look at other gas appliances in the home to see if they are working, which shows whether the home has gas supply Visually check the breaker panel to see if the water heater's breaker has tripped
81	Safety hazard	The unit failed to fully shut off its gas supply the way it is supposed to.	2 safe checks Look at other gas appliances in the home to see if they are working, which shows whether the home has gas supply Visually check the breaker panel to see if the water heater's breaker has tripped
82	Pro required	The control board's programming for gas type and altitude was not set up correctly, or the programming chip has a poor connection.	1 safe check Visually check the breaker panel to see if the water heater's breaker has tripped
90	Safety hazard	The unit detected a blockage in the vent that carries exhaust gases outside.	1 safe check Look at the outdoor vent or flue termination and the combustion air inlet for visible blockage such as leaves, snow, ice, or nests
99	Safety hazard	The fan cannot move air properly through the venting system.	1 safe check Look at the air inlet screen and the outdoor vent termination for visible blockage

Sources

SVC 810 Tankless Troubleshooting Manual, Tankless Gas Water Heaters Second Generation Indoor, Outdoor and Direct Vent (Rheem/Ruud, includes RTG2-42, RTG53, RTG66, RTG74 models) (accessed 2026-07-03)
Rheem RTG2-42 Troubleshooting Manual (mirrors official manual content) (accessed 2026-07-03)

Rheem Performance Platinum / Prestige condensing tankless gas water heaters with digital LCD display (models RTGH-S11i, RTGH-S10i, RTGH-S84i and the SR, CRTGH, RUTGH, CRUTGH variants; also sold as 199,900, 180,000, and 157,000 Btu/hr condensing models). Codes display as a letter followed by three digits, for example A011 or T113.

Code	Severity	What it means	Safe checks
A011	Safety hazard	The water heater tried several times to light the burner but never sensed a flame, so it shut down. A common cause is the gas shut off valve not being fully open.	2 safe checks Look at other gas appliances in the home, such as the stove or furnace, to see if they are working, which shows whether the home has gas supply Visually check the breaker panel to see if the water heater's breaker has tripped
A012	Safety hazard	The burner lit but then lost its flame repeatedly during operation, so the unit shut down. On propane units, this can happen if the propane tank is running low.	3 safe checks Look at other gas appliances in the home to see if they are working, which shows whether the home has gas supply For propane units, look at the tank gauge to see if the propane level is low Visually check the breaker panel to see if the water heater's breaker has tripped
A014	Safety hazard	A safety device called the overheat limiter sensed the unit was overheating, often due to a gas supply or venting problem, and shut off the burner.	1 safe check Look for anything blocking the outdoor vent or the air intake opening
A018	Pro required	Lime and mineral scale have built up inside the heat exchanger. The manual says the unit must be drained and flushed to prevent permanent damage.	None needed
A029	Pro required	The built in condensate trap is full or its water level sensor cannot get a reading, often from a blocked condensate drain line.	1 safe check Look at the condensate drain line, if visible, for kinks, clogs, or a disconnected hose
A031	Pro required	The sensor that measures incoming cold water temperature is not working correctly.	None needed
A032	Pro required	The sensor that measures the heat exchanger temperature is not working correctly.	None needed
A033	Pro required	The sensor that measures the outgoing hot water temperature is not working correctly.	None needed
A035	Pro required	One of the unit's three temperature sensors has a loose or incorrect connection.	None needed
A036	Pro required	The sensor that measures exhaust gas temperature is not working correctly.	None needed
A055	Safety hazard	A motor that adjusts the air and gas mixture valve is not moving correctly.	1 safe check Visually check the breaker panel to see if the water heater's breaker has tripped
A061	Safety hazard	The blower fan is not spinning at the speed the control board expects.	1 safe check Visually check the breaker panel to see if the water heater's breaker has tripped
A063	Pro required	The built in recirculation pump is running but the unit is not sensing water flow. This code only appears on models with a built in recirculation pump.	1 safe check Visually check the breaker panel to see if the water heater's breaker has tripped
A065	Pro required	The valve that controls water volume through the unit is not working correctly.	1 safe check Visually check the breaker panel to see if the water heater's breaker has tripped
A066	Pro required	The valve that controls water bypass through the unit is not working correctly.	1 safe check Visually check the breaker panel to see if the water heater's breaker has tripped
A070	Pro required	The control board's internal computer is not working correctly.	1 safe check Visually check the breaker panel to see if the water heater's breaker has tripped
A071	Safety hazard	The valve that sets the air to gas ratio is not working correctly.	2 safe checks Look at other gas appliances in the home to see if they are working, which shows whether the home has gas supply Visually check the breaker panel to see if the water heater's breaker has tripped
A072	Safety hazard	The part that senses flame detected a flame signal before the igniter was even turned on, which points to a flame sensing fault.	1 safe check Visually check the breaker panel to see if the water heater's breaker has tripped
A082	Safety hazard	The gas type programming chip on the control board has a poor connection or the wrong information for the gas type or altitude in use.	1 safe check Visually check the breaker panel to see if the water heater's breaker has tripped
A090	Safety hazard	The water heater sensed a blockage in the venting system and shut down to prevent a dangerous buildup of exhaust gas.	2 safe checks Look at the outdoor vent and air intake openings for visible blockage such as leaves, snow, ice, or nests Make sure nothing is stored within about 12 inches of the air intake opening
T111	Pro required	A service reminder telling the owner the unit has reached its scheduled maintenance point and needs to be drained and flushed. The unit will eventually shut itself down if this is ignored.	None needed
T113	DIY OK	The water heater is not sensing enough water flow to turn on. It needs at least 0.4 gallons per minute of flow to activate. The manual states this code appears only when water flow is below the 0.4 GPM minimum needed to start the heater, and lists fully opening the faucet or cleaning the user serviceable inline water filter as the first steps before contacting service.	2 safe checks Look to see if the hot water faucet is fully open Clean the external inlet water filter at the cold water connection, which the manual says is safe for the owner to remove and rinse

Sources

Condensing Tankless Water Heater Use and Care Manual with Installation Instructions (AP22745 Rev 04), 199,900 / 180,000 / 157,000 Btu/hr models (accessed 2026-07-03)
IKONIC Tankless Water Heater Technical Training and Service Manual (RTGH-S11i, RTGH-S10i, RTGH-S84i and SR/CRTGH/RUTGH/CRUTGH variants) (accessed 2026-07-03)

Last updated 2026-07-03.