Tankless Water Heater Error Codes: 11, 12 and 10 by Brand

By Ray Bennett · Updated 23 October 2026 · 5 min read · Checked against the makers’ own manuals

Short answer

On Rinnai, Noritz, Takagi and Rheem tankless heaters, 11 means it did not light and 12 means the flame went out, so check the gas is on first. Navien uses E003 and E012 for the same faults. 10 is not shared: an air or exhaust blockage on Rinnai, a warning of abnormal combustion on Takagi. Scale has a different code on each brand that shows one.

A gas tankless water heater shows a number on its controller or its front panel when it stops. The good news is that the ignition and flame codes agree across four brands: 11 and 12 mean the same kind of thing on Rinnai, Noritz, Takagi and Rheem. The bad news is that others do not, and Navien uses a different numbering altogether.

This page brings together what the makers’ own manuals say, as quoted on this site’s brand pages. Every brand-specific line here comes from the document cited on that brand’s page.

For Eccotemp i12-LP or i12-NG, see the Eccotemp i12 error code guide for its E0 to E8 chart and repair limits.

For Marey ECO150 electric units, use the Marey E1 and E3 guide, including its breaker and qualified-electrician limits.

Before you start

What to carry: a torch and a pen. Ten minutes.

Gas or electric? Gas, natural gas or propane. Electric tankless heaters use their own codes: EcoSmart, Stiebel Eltron Tempra Plus and older DHC-E and Eemax LavAdvantage and AccuMix II.

Read the whole code. Takagi shows each fault as a three digit code, a two digit code or a count of red flashes, depending on the model. Rheem’s condensing models add A0 in front, so 11 becomes A011.

Note it before you reset. Rinnai keeps a history, but write the code down anyway before switching anything off.

Where you stop. If you smell gas, turn the heater off, do not touch electric switches, and call the gas supplier from outside.

Thermal fuse codes. Rinnai’s and Noritz’s 14 is a thermal fuse, and Noritz says it breaks in an extreme overheat and cannot be reset. That is a service call.

11 or 12 again and again. Once the gas is definitely on, Rinnai and Takagi both move on to gas pressure and the igniter. That is technician work.

The codes that agree

11 and 12 mean ignition and flame on four brands, and Navien's E003 and E012 are the same faults. 61 is the fan on four brands.

Check 1Free, ten minutes

Work the gas codes

11: no ignition. Rinnai, Noritz and Takagi call it no ignition or ignition failure, and Rheem’s 11 is the gas shut off valve not fully open. Check the gas is on at the heater and the meter, and on propane, that the tank is not empty. Navien’s E003 is the same fault.

12: the flame went out. Rinnai calls it flame failure, and Noritz and Takagi flame loss. Rheem’s 12 is gas service interrupted or propane running low. Navien’s E012 is flame loss.

After gas work. Rinnai lists bleeding all air from the gas lines among its fixes for 11 and 12.

61: the fan. Rinnai’s combustion fan, Takagi’s fan motor, Rheem’s blower motor, and the fan motor on Noritz Pro Series models. That is a service call.

The codes that do not agree

Code	What it means, by brand
10	Rinnai: air supply or exhaust blockage. Takagi: a warning that abnormal combustion, 991, is coming.
90 and 99	Rheem: air intake or vent blocked. Takagi 99: abnormal combustion. Noritz 90: a combustion abnormality.
31	Rinnai: burner sensor. Takagi: the output thermistor. Rheem: the inlet water thermistor.
Scale	Rinnai: LC. Rheem: 1L. Noritz premix models: C1 and a number.
Condensate	Rinnai: 25. Noritz: 29. Rheem: A029.

Air, scale and water

The air, scale and condensate faults carry a different number on each brand.

Check 2

Work the owner checks

Air and exhaust codes. Rinnai’s 10, Rheem’s 90 or 99 and Takagi’s 101 and 991 all start with the vent and air intake outside: nests, leaves, snow or trash. Takagi adds a backflow preventer fitted backwards.

Scale codes. LC on Rinnai, 1L on Rheem and C1 on Noritz premix models all mean lime is building up in the heat exchanger. The fix is a flush: how a tankless heater is flushed.

Condensate codes. On condensing models, Rinnai’s 25, Noritz’s 29 and Rheem’s A029 mean the condensate is not draining. Check the drain line for a block or ice.

Overheating on Navien. Navien’s E016 and E030 start with cleaning the inlet filter and flushing.

Find your heater’s full list

Brand	How it shows codes	The full list
Rinnai	Two digit codes, LC for scale	Rinnai codes
Noritz	Two and three digit codes	Noritz codes
Takagi	Three digit, two digit or red flashes	Takagi codes
Rheem	Two digit, or A codes on condensing models	Rheem tankless codes
Bosch	A letter and a digit, such as EA or C2	Bosch tankless codes
Navien	E and a three digit number	Navien codes
Bradford White Infiniti GS and GR	Er and a two digit number, hard or soft lock	Bradford White tankless codes
EcoSmart, electric	E codes, or letter and number messages	EcoSmart codes

When there is no code

Check 3Free, ten minutes

Check the flow and the water

Hot, then cold. A tap opened too little can drop below the flow the heater needs to stay lit: why a shower goes cold.

No hot water anywhere. Start with the basics: when a whole house has no hot water.

Questions people ask

What does error code 11 mean on a tankless water heater?

On Rinnai, Noritz and Takagi, the heater did not light. On Rheem, the gas shut off valve is not fully open. Check the gas is on, and the propane tank if you have one.

What does error code 12 mean?

The flame lit and went out, or the gas supply dropped. Check the gas first, then the vent. If it returns with the gas on, it needs a technician.

What does code 10 mean?

On Rinnai, an air supply or exhaust blockage. On Takagi, 10 or 101 warns that abnormal combustion is coming. Check the vent and air intake outside.

What is the scale code on a tankless heater?

LC on Rinnai, 1L on Rheem, and C1 with a number on Noritz premix models. All three mean it needs flushing.

Do Navien codes match the others?

No. Navien uses E and a three digit number, such as E003 for ignition failure and E012 for flame loss.

How do I reset a tankless water heater?

It depends on the code and brand. Noritz gives a short unplug for some codes, but gas, vent and scale codes need the cause fixed first.

Sources: The makers' own documents, as cited on this site's brand pages: Rinnai, Noritz, Takagi (A.O. Smith), Rheem and Navien