There’s nothing quite as jarring as stepping into the shower, expecting a relaxing stream of hot water, and being met with an icy blast. You rush to your tankless water heater, expecting to see a pilot light out, but instead, you’re greeted by a digital display flashing a mysterious number. That blinking code is designed to tell you exactly what is wrong.

At Any Hour Electric, Plumbing, Heating & Air, we know that deciphering these codes is the first step to getting your hot water back. Whether you own a Rinnai, Navien, Rheem, or Noritz unit, this guide will help you understand what your system is trying to tell you and when you need to call in the pros.

What Do Tankless Water Heater Error Codes Mean?

Modern tankless water heaters are smart appliances. Unlike the old tank-style heaters that would just stop working silently, tankless units are equipped with internal computers and sensors. These sensors constantly monitor water flow, gas pressure, exhaust ventilation, and water temperature.

When one of these sensors detects a reading that is outside the safe operating range, the computer shuts the system down to prevent damage and displays an error code.

Think of these codes as a “Check Engine” light for your home’s plumbing. They don’t always mean the unit is broken. Sometimes, they’re just asking for maintenance. However, ignoring them can lead to total system failure.

Why Do Arizona Homes See Specific Error Codes?

If you’re a homeowner in the Grand Canyon State, you’re likely battling two major enemies of plumbing: hard water and dust.

Hard Water and Scale

Arizona has some of the hardest water in the country. This water is packed with minerals like calcium and magnesium. When this water is heated rapidly, which is exactly what a tankless heater does, those minerals precipitate out and stick to the walls of your heat exchanger. This is called “scale.” Scale acts like an insulator, making it harder for the burner to heat the water. Eventually, the unit overheats or detects a blockage, triggering a code.

Dust and Venting

Our monsoon seasons and general desert environment kick up a lot of dust. Since tankless water heaters pull in fresh air for combustion, clogged intake filters or vents are common issues here. If the filters are clogged, the unit can’t heat water.

What Are the Most Common Ignition and Flame Error Codes?

The most frequent panic-inducing codes are related to the fire itself. If the unit tries to light the burner and fails, or if the flame goes out while running, you will see specific codes.

Common Codes:

• Rinnai / Rheem / Noritz: Code 11 (Ignition Failure) or 12 (Flame Failure)
• Navien: E003 (Ignition Failure) or E012 (Flame Loss)

What is happening?

• Code 11 / E003: The system tried to light the gas but couldn’t. This usually means there is no gas getting to the burner, the igniter isn’t sparking, or the gas valve is closed.
• Code 12 / E012: The system lit the fire, but it went out immediately. This is often caused by a dirty flame sensor (which can’t “see” the fire), low gas pressure, or a venting issue.

Troubleshooting Tips:

• Check that your gas supply is turned on. Did someone accidentally bump the valve?
• Check your other gas appliances. Is the stove working? If not, you may have a utility outage.
• If you have propane, check your tank level.

What Does an Exhaust or Venting Error Code Indicate?

Your tankless water heater needs to inhale fresh air and exhale exhaust fumes. If either of these paths is blocked, the unit will shut down immediately to prevent carbon monoxide buildup in your home.

Common Codes:

• Rinnai: Code 10
• Navien: E030 (Exhaust Overheat/Blockage)
• Rheem: Code 13
• Noritz: Code 90

Causes in Arizona:

• Bird Nests: Birds love the warmth of exhaust vents in the winter.
• Dust Accumulation: Intake screens can get clogged with desert dust.
• Debris: A recent storm may have blown leaves or trash into the vent termination on your roof or sidewall.

Safety Warning:

Never ignore a venting code. These are critical safety features. If you suspect a blocked vent, ensure the unit is off and visually inspect the external vents if safely accessible.

Why Am I Seeing Scale Buildup or Maintenance Codes?

This is the “Arizona Special.” Because of our hard water, tankless manufacturers often include codes specifically to tell you that the unit is choking on mineral deposits.

Common Codes:

• Rinnai: Code LC or 00 (Scale Build-up)
• Navien: E016 (Overheating often caused by scale)
• Rheem: Code 29 (Heat Exchanger Outlet Temp Too Low – often scale related)

What is happening?

The heat exchanger is coated in rock-hard minerals. The unit has to work twice as hard to heat the water, causing internal temperatures to spike.

The Fix:

You likely need a tankless flush (descaling). This involves pumping a food-grade vinegar or descaling solution through the unit for 45-60 minutes to dissolve the minerals. In Arizona, we recommend doing this once a year. If you’re seeing the code, it’s already overdue.

What Should I Do If I See a Sensor or Electrical Error?

Sometimes the computer brain of the unit gets confused, or a specific sensor fails. Power surges, which are common during our storms, can also fry internal fuses.

Common Codes:

• Sensors: Codes starting with 3, 4, or 5 (e.g., Code 31, 32 for temperature sensors).
• Electrical: Code 70, 71, or 72 (PC Board or Solenoid issues).

Troubleshooting:

• Check for loose wires if you recently moved the unit (unlikely).
• Check your breaker box to ensure the unit has clean power.
• These codes almost always require a professional diagnosis to replace the specific sensor or circuit board.

How Can I Reset My Tankless Water Heater?

Before calling for service, it’s often worth trying a “soft reset” to see if the error was just a glitch (like a momentary drop in gas pressure).

1. Turn off all hot water taps in the house.
2. Locate the power button on the remote control panel or the front of the unit.
3. Press the “Off” button, wait 10 seconds, and then press “On”.
4. Open a hot water tap to see if the unit fires up.

Note: Unplugging the unit from the wall outlet can also work as a “hard reset,” but consult your owner’s manual first. If the code comes back immediately, you have a hard fault that needs repair.

When Should I Call a Professional for Water Heater Repair?

While a simple reset works for glitches, most error codes indicate a physical problem that needs a physical fix. You should call Any Hour Electric, Plumbing, Heating & Air if:

• You smell gas. (Turn off the gas immediately and call us or the utility company).
• The code returns after resetting. This means the problem is persistent.
• You see Code LC / 00. You need a professional descaling service.
• You hear loud rumbling or banging. This is “kettling” caused by severe scale buildup.
• You are not comfortable working with gas or electricity. Tankless units combine water, gas, and high-voltage electricity, which is a dangerous mix for DIY attempts.

Conclusion

Your tankless water heater is a workhorse, providing endless hot water for your Arizona home. But when it flashes an error code, it’s asking for help. By understanding what these codes mean, especially the ones related to our local hard water issues, you can make informed decisions about maintenance and repair.

Don’t let a blinking light leave you in the cold. Whether it is a simple sensor error or a much-needed descaling service, our team is ready to help.

Need help clearing that error code?

Contact Any Hour Electric, Plumbing, Heating & Air today to schedule your tankless water heater repair.

Tankless Water Heater Error Codes Frequently Asked Questions

Q: What is the most common error code for Rinnai tankless heaters?

A: Code 11 (Ignition Failure) and Code 12 (Flame Failure) are the most common. They usually indicate an issue with the gas supply, a dirty flame rod, or a clogged intake vent. In Arizona, Code LC (Scale Buildup) is also very frequent due to hard water.

Q: Can I descale my tankless water heater myself?

A: Yes, if you have the right equipment (a submersible pump, bucket, hoses, and descaling solution) and isolation valves installed on your unit. However, the process involves handling acidic solutions and ensuring the system is flushed correctly. Many homeowners prefer to have a professional handle it to ensure it’s done safely and thoroughly.

Q: How do I read the error code on a tankless water heater without a screen?

A: Some older or budget-friendly models use flashing LED lights instead of a digital screen. You will need to count the pattern of flashes (e.g., two short blinks followed by a pause) and compare it to the “Troubleshooting” section in your owner’s manual.

Q: Why does my tankless water heater turn off during a shower?

A: This is often due to a “flow sensor” error or the “cold water sandwich” effect. If the water flow drops below the activation threshold (usually 0.5 gallons per minute), the heater turns off. This can happen if you are using a water-saving showerhead that restricts flow too much.

Q: Does Any Hour Services repair all brands of tankless water heaters?

A: Yes! Our technicians are trained to service and repair all major brands found in Arizona homes, including Rinnai, Navien, Rheem, Noritz, Takagi, and Bosch.