Tankless Water Heater Error Codes: Top 10 Cheat Sheet

Your tankless water heater isn’t delivering hot water, or you hear an annoying beeping sound. When you approach the unit, you see an error code on the digital display. But “11”, “29” and “E003” don’t actually tell you what’s wrong- so what do these error codes mean?

Don’t worry: we’ll answer all your questions in one handy cheat sheet.

At Mother, we’re passionate about energy-saving plumbing tech like tankless water heaters, that deliver on-demand hot water and lower insurance claim risks for your home. We looked at 3 years of service data to determine the top 10 tankless error codes seen most often by homeowners.

We’ll cover frequent error codes from Rinnai, Navien, Rheem, and A.O. Smith/State Water Heaters, as well as what they mean and how to fix them. For a list of every Rinnai, Navien and Rheem tankless error code, visit our recent guide. 

Need a tankless error code resolved in Dallas? Call Mother 24/7 for prompt, licensed tankless repairs- use priority scheduling to skip the waiting list.

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3 Most Common Causes of Tankless Error Codes

Our Master Plumbers identified the 3 most common reasons homeowners get an error code on their tankless water heater:

1. No ignition. “Tankless units need three things in order to light properly,” says our Master Plumber Dillon Ashton. “Gas, air, and water flow.” Lose just one of these components, and you’ll face ignition issues.
2. Air or vent blockage. Tankless vents are blocked by a variety of things- from bird’s nests to pipe insulation that blocks the venting. It’s a common problem.
3. Flame loss. Scale buildup on your heat exchanger, flow sensor or temperature sensor causes flame loss easily. Regular descaling maintenance fixes the issue.

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Your Tankless Error Code Cheat Sheet

Don’t have time to read the full article? Here’s a handy cheat sheet of the 10 most frequent error codes displayed on Rinnai, Navien, Rheem and A.O. Smith units:

Tankless Brand

Error Code

What It Means

Rinnai

​

11

Ignition failure

12

Flame failure

10

Air supply blockage

Navien

E003

Ignition failure

E012

Flame loss

E030

Overheating exhaust

Rheem

11

Ignition failure

12

Flame failure

29

Heat exchanger outlet temperature too low

A.O. Smith (State)

E02

Ignition failure

Don’t see your tankless error code listed? Check out our complete guide, which includes every tankless error code on Rinnai, Rheem and Navien systems.

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Common Rinnai Tankless Water Heater Error Codes

Homeowners commonly see 3 error codes on their Rinnai tankless units- 10, 11 and 12. Here’s what they mean- and how to address them- in order of frequency.

Rinnai error code 11

What it means: No ignition

Your tankless water heater is attempting to light on startup, but something’s keeping it from doing so. 

Gas, air and water flow are needed for ignition to occur. Here’s the most common reason each component would fail:

1. Gas: Low gas flow stops automated ignition in its tracks. Check if the gas is turned off- if not, there is a blockage in your gas line.
2. Air: A blocked vent or intake prevents enough oxygen for the burner to light.
3. Water: Clogged water filters create low water flow, and your unit may not activate the ignition process.

The best fix: Call a licensed plumber.

Other than cleaning your water inlet filter, there’s not much DIY work to be done here. It’s risky for homeowners to attempt repairs on the gas line or to clear a blocked vent- any damage done to these components will void your product warranty.

Get Rinnai-specific steps to descale your tankless in our updated guide!

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Rinnai error code 12

What it means: Flame failure

The ignition process started out fine, but something caused the flame to get snuffed out during operation. This error code is usually persistent- flame failures are rarely a one-time occurrence.

There are 2 primary reasons why your Rinnai tankless experiences flame failure:

1. Dirty flame rod: If the sensor is dirty, it won’t detect a flame properly. The flame is extinguished as a failsafe.
2. Low gas pressure: There isn’t enough incoming gas to support the flame. This is a less common situation, as there was enough gas to spark ignition.

The best fix: Clean your flame rod

Shut off the gas and power to your tankless before attempting any cleaning. Remove the front cover on your Rinnai to reach the burner assembly. Gingerly disconnect the flame rod wire, then clean carbon buildup off the rod itself with very fine sandpaper or a cloth. 

If you feel uncomfortable disconnecting the flame rod wire, that’s normal- it’s a delicate process. Call your trusted plumber if you need to.

If you experience flame failure after cleaning the rod, call a licensed plumber to diagnose potential gas line issues.

No hot water from your tankless? Our 2-minute Fast Plumbing Answers guide breaks down the most common reasons why.

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Rinnai error code 10

What it means: Air supply blockage

Either your Rinnai isn’t getting enough incoming air, or it can’t vent exhaust properly.

This is a very common problem in fall and winter months, where the intake vent, internal fan and exhaust venting are easily blocked by these items:

• Bird’s nests
• Leaves
• Lint
• Ice and debris

The best fix: Call a licensed plumber.

The problem is resolved by opening up the vent inside the home, or accessing and clearing debris on the roof. As with ignition issues, any damage caused to your venting system or internal fan voids your product warranty- so DIY repairs aren’t recommended.

Common Navien Tankless Error Codes

The three most common error codes on Navien tankless units are E003, E012 and E030. They are nearly identical to the 3 most frequent Rinnai error codes, just with different numbers.

Navien error code E003

What it means: Ignition failure

As with Rinnai code 11, the automated Navien ignition system failed on startup. 

The same 3 potential reasons for ignition failure exist: low gas flow, lack of sufficient air intake, or a low water flow caused by a dirty inlet filter.

The best fix: Call a licensed plumber.

Navien is notorious for voiding warranties based on online reviews from owners who called their customer support team. Don’t DIY anything on a Navien system- they don’t even want homeowners trying to install their units.

Tankless won’t ignite? Dive deeper into the issue and get fast answers with our 2-minute guide to this common problem.

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Navien error code E012

What it means: Flame loss

Your Navien tankless was able to achieve ignition, but lost its flame during the heating or hot water delivery process.

As with Rinnai error code 12, you’re dealing with a dirty flame rod or low gas pressure. In the case of Navien systems, it’s incredibly likely your issue is scale and carbon buildup on the flame rod sensor.

Internal components in Navien tankless units have a tough time handling scale accumulation and debris. In our last 3 years of service calls, every Navien flame loss error code was caused by buildup on the flame rod.

The best fix: Clean your flame rod.

Shut off power and gas to the unit before anything else. Remove the front cover and casing on your Rinnai tankless to access the burner area.

Then, unplug the sensor wire from the system’s igniter and flame rod assembly. Take out the mounting screws holding the assembly in place, and remove the assembly from the unit. Fine grit sandpaper or an emery cloth are best for cleaning.

We strongly suggest calling a licensed plumber to handle flame rod cleaning. As stated, Navien’s rather quick to void product warranties for damage caused by DIY repairs.

Navien error code E030

What it means: Overheating exhaust

The system detects an abnormally high temperature or blockage in the exhaust.

Of the Navien error codes listed, this is the most critical. High heat in the exhaust presents a hazard to internal components, as well as a flame risk around debris or loose materials.

Sadly, there are a myriad of potential reasons for the E030 error code that make diagnosing the problem tough for homeowners:

• Blocked venting
• Your vent run is too long (over 75 feet)
• Your vent run has too many elbows
• Clogged heat exchanger
• Clogged filters

The best fix: Call a licensed plumber.

It’s extremely tough for homeowners to figure out precisely what caused Navien code E030. The issue could be an internal component (heat exchanger), a filter problem, vent blockages inside or outside your home, or an improperly installed vent run.

Call a plumber if you see this error code- you’ll save hours of head-scratching.

Common Rheem Tankless Water Heater Error Codes

The most frequent error code displays on Rheem tankless water heaters are 11, 12 and 29. Many Rheem and Rinnai tankless error codes are identical (11 and 12 in particular).

Rheem error code 11

What it means: Ignition failure

Your Rheem tankless failed to ignite on system startup.

As with Rinnai and Navien units, this means one of three things:

1. Low gas intake due to a gas line issue or blockage.
2. Low air due to a blocked vent or intake that limits oxygen.
3. Low water intake due to a dirty filter or inlet that creates low water flow.

The best fix: Call a licensed plumber.

We’ll repeat our advice from other products above- attempting to repair or clean the igniter and ignition assembly in your Rheem tankless is a surefire way to void your product warranty. Don’t try it unless you’re a plumber yourself, or you’re exceptionally handy.

Rheem error code 12

What it means: Flame failure

The ignition process worked just fine, but your flame went out shortly afterwards due to a gas or oxygen problem.

We’ve talked about dirty flame rods causing flame failure, due to a buildup of carbon and mineral scaling. But many Rheem systems also experience flame loss due to an improperly sized gas line.

Many homeowners neglect to upsize their gas lines when converting to a tankless water heater. This creates an environment where there’s just enough gas to ignite, but not enough to maintain a flame.

The best fix: Check your existing gas line.

Check the size of your existing gas line- it may be undersized for your current Rheem tankless unit. If you aren’t sure about sizing, call the plumber who installed your tankless unit- they should have the information on file. 

That call will reveal one of two things:

1. The original installer didn’t upsize your gas line, or
2. It’s the right size, and you have an intake issue or dirty flame rod.

Either way, it’s best to call a licensed plumber to correct the issue. If your original plumber didn’t upsize the gas line- get a new plumber to handle the repairs.

Not sure what size gas line you need? Check our quick guide for expert advice on how to “right-size” your natural gas lines.

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Rheem error code 29

What it means: Heat exchanger outlet temperature too low

The tankless unit can’t reach your desired temperature. This error code occurs more frequently on Rheem tankless systems than other brands.

Rheem code 29 usually signals a clogged neutralizer. The neutralizer treats the condensate produced by condensing tankless units- reducing its acidity before discharging it from the system. While this process prevent pipe corrosion, the neutralizer on Rheem units clogs a bit more often than usual.

If it’s not your neutralizer, there may be excess scale buildup on your heat exchanger.

The best fix: Call a licensed plumber.

Schedule an inspection of your Rheem condensing tankless water heater’s neutralizer. If that’s the issue, your plumber will clean it- don’t attempt to do it yourself, as this component handles highly acidic condensate.

If the neutralizer is fine, ask your plumber for descaling service with a particular focus on the heat exchanger.

The Most Common A.O. Smith Tankless Error Code

The most common error code on A.O. Smith (and State Water Heaters) tankless units is far and away code E02.

A.O. Smith and State Water Heaters error code E02

What it means: Ignition failure

We won’t repeat ourselves too much here. Ignition failure is caused by a lack of sufficient gas, air or water.

In A.O. Smith products (which also covers State Water Heaters), the most common reason for ignition failure is an air intake blockage. 

The best fix: Check your air intake first, then call a licensed plumber.

The first place you should check are the air intake screens- you’ll likely notice lint or other debris clogging them.

If you don’t see a blocked air intake screen, call a plumber- there’s a low water flow or gas line issue.

Stay ahead of the game with a smart tankless maintenance plan. Our Master Plumbers created the easiest checklist you’ll find.

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Tankless Error Code in Dallas? Call Mother 24/7

Most error codes on popular tankless water heater products are caused by one of three issues: ignition failure, flame loss, or a problem with your venting and exhaust system. 

The most common reasons for these issues deal with scale buildup on internal components (especially your heat exchange or flame rod), blocked vents and inlet screens. Some homeowners may have an improperly sized gas line that isn’t delivering sufficient gas.

It’s best to call a licensed plumber to address these issues- damage caused by DIY repairs voids your product warranty. (This is especially true for Navien products.)

Dallas: fix that tankless error code now! Call Mother 24/7- we’ll stop that beeping alarm and restore hot water to your home, fast.

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