What do Rheem 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].

This table paraphrases Rheem's SVC820 tankless gas troubleshooting manual, which covers Rheem and Ruud non-condensing and condensing units, indoor and outdoor^[1]. It is our wording, not Rheem's. Newer Rheem platforms may use different codes; check your unit's manual. Rheem technical service is listed at 1-800-432-8373^[1].

Rheem tankless code table

Code	What it means	Safe homeowner check	Call a pro when
No code, no hot water	Display shows the setpoint but water stays cold	Power off and on once; clean the inlet water filter	Still cold: possible swapped hot and cold lines or a plumbing cross-over
P1	Hot water is not being delivered	Reset once; clean the inlet filter	It returns
1L	Scale building up in the heat exchanger; flush to avoid damage	Schedule a flush (Rheem sells a flush kit)	You prefer not to flush it yourself
03	Communication failure between linked units or a manifold controller (multi-unit installs)	None	Always
05	Indoor units: flame rod sensing poor combustion (warning)	Check the outside vent terminal	It returns: gas and vent diagnosis
10	Vent or blower problem, such as running before venting was installed or low airflow. Hard lockout	Check the vent terminal for blockage	Always: reset procedure and blower diagnosis
11	No flame detected during ignition	Gas valve open and gas service on	Still no flame: gas pressure, altitude setting, igniter or board
12	Flame lit, then was lost	Confirm gas supply	It returns
13	Indoor units: poor combustion detected. Hard lockout	None	Always
14	Overheat limiter tripped	Stop resetting	Always
15	Water or heat exchanger hit about 207 F for over 15 seconds	Schedule a flush (scale is a common cause)	Always if it returns: sensor and gas checks
16	Outlet water above the setpoint	None	Always: outlet sensor or bypass valve
24	Remote control buttons held more than 20 seconds	Release the buttons and retry	It repeats: remote may be faulty
29	Condensing units: condensate not draining, or heat exchanger too cold for over 3 minutes	Check the condensate line for clogs or ice	It returns: trap, neutralizer or sensor service
31, 32, 33, 34	Temperature sensor fault: inlet (31), heat exchanger (32), outlet (33), ambient (34)	None	Always
35	Sensors plugged into the wrong place or poorly connected	None	Always
51, 80	Gas control valve fault: flame still present after hot water demand stopped	Shut off gas to the unit	Always, right away
52	Modulating gas valve fault	None	Always
61, 79	Blower fault: wrong speed (61) or motor current fault (79)	None	Always
65, 66	Water volume control valve fault (65) or water bypass valve fault (66)	None	Always
71	Gas control valve inlet solenoid fault	None	Always
72	Flame rod senses flame before ignition (false flame)	None	Always
76	Remote control not talking to the board	None	Always
82	Control board program chip fault	None	Always: board replacement
90, 99	Vent blockage detected during purge, or the unit ran before the vent was installed. 99 is a hard lockout	Check the outside vent terminals	Always for 99; for 90 if it returns
92	Condensing units: neutralizer needs service soon; the unit keeps running for now	Schedule service	Book it before it becomes 93
93	Condensing units: will not run until the neutralizer is serviced	None	Always

Source: Rheem SVC820^[1], paraphrased.

Codes to treat as urgent

• 51 and 80 mean the gas valve may not be closing when it should. Shut off the gas to the unit and call^[1].
• 14, 15 and 16 are temperature problems. Repeated resets can mask a real overheat.
• 10, 13 and 99 are venting or combustion lockouts. Do not try to bypass them.

"No code, no hot water" is common on new installs

Rheem's manual lists two causes worth knowing before you pay for parts: hot and cold lines swapped at installation, and a plumbing cross-over, such as a failed single-handle faucet cartridge or mixing valve letting cold water into the hot line^[1]. A plumber can isolate fixtures to find a cross-over.

Scale and condensate: the maintenance codes

1L appears before scale does damage. 92 warns that the condensate neutralizer needs service, and 93 follows if it is ignored, shutting the unit down^[1]. HomeGuide's 2025 range for a tankless flush and descale is $75 to $300^[3].

When to call a pro

• Codes 51 or 80: shut off the gas to the unit first.
• Any hard lockout (10, 13, 99) or overheat code (14, 15, 16).
• Any sensor, valve, blower, remote or board code.
• No hot water with no code after a reset and a clean inlet filter.