Rheem Tankless Error Codes: What Each Code Means

All Rheem codes

Code	Meaning
00	Continuous combustion for more than one hour Full guide
03	Communication failure between units, remote or manifold controller Full guide
05	Improper combustion detected by the flame rod (warning) Full guide
10	Air supply or exhaust blockage (hard lockout) Full guide
11	Ignition failure Full guide
12	Flame failure Full guide
13	Poor combustion detected by the flame rod (indoor units) Full guide
14	Overheat safety tripped Full guide
15	Heat exchanger or hot water temperature too high (boiling safety) Full guide
16	Outlet water temperature above the set point (over temperature warning) Full guide
21	Air intake filter switch fault (earlier models) Full guide
24	Remote control buttons held too long, or operational switch fault Full guide
29	Condensate not draining (condensing models) or heat exchanger temperature too low Full guide
31	Inlet water temperature sensor (thermistor) fault Full guide
32	Heat exchanger thermistor fault Full guide
33	Outlet (outgoing water) thermistor fault Full guide
34	Ambient or combustion air temperature sensor fault Full guide
35	Improper thermistor connection Full guide
51	Gas valve fault: flame detected after shutdown (current) / gas inlet solenoid valve fault (earlier) Full guide
52	Modulating gas valve (PGFR) fault Full guide
61	Blower (combustion fan) motor fault Full guide
65	Water volume control valve fault Full guide
66	Water bypass valve fault Full guide
71	Gas inlet solenoid valve fault Full guide
72	Flame rod fault: flame sensed before ignition Full guide
76	Remote control communication fault Full guide
79	Blower (fan) motor current fault Full guide
80	Gas cut-off failure: flame detected after the unit turned off Full guide
82	Control board program chip fault (current) / gas type data failure (earlier) Full guide
90	Vent blockage detected before ignition Full guide
92	Neutralizer needs replacing soon (warning, condensing models) Full guide
93	Neutralizer must be replaced; unit will not operate (condensing models) Full guide
1L	Lime (scale) buildup detected in the heat exchanger Full guide
99	Vent blockage detected after shutdown / blocked flue (hard lockout) Full guide
P1	Not enough water flow to fire the burner (warning) Full guide

Many Rheem tankless codes match Rinnai's, especially the ignition and flame codes. Like most tankless brands, Rheem shuts the burner off and shows a code when a safety check fails, and some codes are only warnings that let the unit keep running.

How to reset a Rheem code

Close all hot water taps.
Turn the unit off and back on at the controller.
Open a hot water tap and see whether it fires.

If the same code returns, the cause is still there. Do not keep resetting combustion or overheat codes.

What homeowners can check

Gas supply: valve open, other gas appliances working, propane tank level.
Vent and air intake terminals outside, for blockages.
The cold water inlet filter, which can clog and reduce flow.
The condensate drain and neutralizer on condensing models.
When the unit was last descaled.

When to call a technician

Ignition parts, gas pressure, fans, sensors and the control board all sit inside the sealed unit. If a code returns after the checks above, call a licensed installer.

Common questions

Are Rheem and Rinnai error codes the same?

Several are, including 11 for ignition failure and 12 for flame failure, but not all of them. Use the code list for your brand.

What does P1 mean on a Rheem tankless?

P1 means the water flow is too low for the unit to fire. A clogged inlet filter or a partly closed valve is a common cause.