Rheem Tankless Code 11 (Ignition Failure): Causes and Fixes

Code 11 is the ignition failure code on Rheem tankless heaters, and it is one of the most common codes Rheem owners see. Many Rheem and Rinnai codes match, and 11 means the same thing on both.

The heater needs gas, air and enough water flow to fire. Code 11 means one of the three was missing, or a part in the ignition system did not do its job.

If you smell gas, do not reset the unit or touch any switches. Leave the building and call your gas utility from outside.

What to check first

Make sure other gas appliances work and the gas valve to the heater is fully open.
On propane, check the tank level.
Look at the vent and air intake terminals outside and clear any blockage.
Clean the cold water inlet filter; low flow can stop the burner from firing.
Turn the unit off and back on at the controller and open a hot tap.

Common causes

Gas supply or pressure

A partly closed valve, air in a new gas line, an empty propane tank, or a gas line too small for the heater's demand.

Air and venting

A blocked intake or exhaust, or dust built up inside the unit, keeps the burner from lighting properly.

Ignition parts

A worn igniter, a dirty flame rod or a failing gas solenoid valve. These are inside the sealed unit and are a job for a technician.

When to call a technician

If gas, vents and the filter check out and code 11 keeps returning, have the unit serviced. Working on gas and ignition parts yourself can void the warranty.

Common questions

How do I reset Rheem code 11?

Turn the unit off at the controller, wait a moment and turn it back on, then open a hot tap. If the gas supply was the problem and it is fixed, the unit should light.

Is Rheem code 11 the same as Rinnai code 11?

Yes, both mean ignition failure, and the checks are very similar.

Other Rheem codes

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