If your Noritz tankless water heater has been flashing an error code lately, don’t panic—it’s your system’s way of telling you something needs attention. Understanding these codes can help prevent further damage, keep your home running efficiently, and determine whether it’s time to call in a professional. Here's a helpful breakdown of the most common Noritz error codes and what they typically indicate.
Understanding Noritz Tankless Water Heater Error Codes: What They Mean and What to Do
When Your System Says, “It’s Time for Service”
Error Code 05
This is a friendly nudge from your unit that it’s time for a professional check-up. It’s not a malfunction—yet—but resetting it without service could lead to a premature failure. Schedule service to keep things running smoothly.
Ignition & Combustion Issues
Error Code 10
Your unit has noticed that combustion is lingering after it should’ve stopped. This could be due to oil or grease on the burner. Try powering the unit off and back on—if the issue persists, let a pro inspect it.
Error Code 11
Your water heater failed to ignite. Check for proper gas pressure and look for anything blocking air flow. Make sure the ignition rod is clean and wiring is intact.
Error Code 12
This means the flame is too weak. Poor airflow or a dirty flame sensor is usually to blame. A good cleaning or part replacement often solves this one.
Error Codes 59, 90, 91, 902, 903, 908, 99
All these errors point to gas combustion issues—anything from low BTU input to improper air-to-fuel mixture. Clean vents, verify gas pressure, and make sure the system is getting adequate airflow. Still seeing issues? It’s time for professional help.
Overheating & Temperature Concerns
Error Code 16
Your unit is running too hot—usually a result of scale buildup from hard water. A descaling flush typically fixes this, followed by a power reset (unplug for 20 seconds).
Error Code 20
The high-limit safety feature has been triggered. This can also be due to scale buildup, so a descaling service is a smart first step.
Error Codes 941 & 942
These point to exhaust temperatures getting too high. Clear out air blockages and reset the unit. If that doesn’t fix it, call for service.
Overheating & Temperature Concerns
Error Code 16
Your unit is running too hot—usually a result of scale buildup from hard water. A descaling flush typically fixes this, followed by a power reset (unplug for 20 seconds).
Error Code 20
The high-limit safety feature has been triggered. This can also be due to scale buildup, so a descaling service is a smart first step.
Error Codes 941 & 942
These point to exhaust temperatures getting too high. Clear out air blockages and reset the unit. If that doesn’t fix it, call for service.
Thermistor & Component Failures
Error Codes 31, 32, 33
These codes signal a thermistor failure—on the cold inlet, hot outlet, or heat exchanger. A faulty sensor will need replacement.
Error Codes 61, 65, 66, 67
These errors involve moving parts like fan motors and flow control valves. If these are faulty or blocked, they’ll need replacement after inspection.
Error Codes 70–73
These point to deeper electronic or programming issues. A reset might work, but improper voltage or circuit board issues are often involved. These should be handled by a licensed technician.
Condensate and Water Flow Issues
Error Code 29
This means the neutralizer isn’t draining properly. Check the condensate line for obstructions or improper slope.
Error Code 45
Your unit thinks there’s a water leak. If one isn’t visible, try unplugging the unit for 30 seconds to reset it. If the code remains, shut off the inlet valve and call for service.
Scale Buildup & Long-Term Maintenance
Error Code CF1–CF4
These codes show that the heat exchanger is starting to scale up. A professional flush following the owner’s manual can restore efficiency.
Error Code CF5–CFF
If the unit detects heavy scale buildup repeatedly, it may lock itself as a safety measure. At this point, you’ll need to flush the system thoroughly and possibly contact a technician to reset it properly.
Error Codes 92 & 93
Your neutralizer has reached the end of its service life. Replace it and reset the burner timer.
Communication & Remote Control Issues
Error Code 760
This typically means there’s a wiring issue with the remote control. Make sure only one remote is connected and all wires are secure. A reset often clears it up.
Error Code F76
This appears when two tankless units using a Quick Connect cord aren’t communicating properly. Make sure only one controller is in use and reset the unit.
While some of these error codes can be resolved with a simple power cycle or filter cleaning, others signal deeper issues that need a licensed professional’s touch. At Advanced Plumbing Systems, we help La Crosse homeowners get the most out of their tankless water heaters. Whether it’s routine maintenance, part replacement, or a full diagnostic, we’re here to keep your hot water flowing without interruptions.
Need help with a Noritz water heater issue? Contact us today to schedule expert service and get your system running like new.