Tankless Water Heater Troubleshooting Guide

Need help interpreting tankless water heater error codes? This comprehensive tankless water heater troubleshooting guide explains how to use Rheem, Noritz, Bosch and Rinnai error codes to fix your water heater.

Troubleshooting Tankless Water Heater Error Codes

If you have a tankless water heater, you’ve made a wise investment that will deliver endless hot water for 20+ years. Tankless water heaters need far less in the way of maintenance and servicing than traditional tank water heaters, but they still do need to be maintained, and when they have problems, it’s important to know what to do.

Rinnai Error Codes

We’re huge fans of Rinnai tankless systems! Your Rinnai tankless water heater is a smart water heater, meaning it is equipped with a self-diagnostic tool that continuously monitors if the unit is functioning properly. When something goes wrong, the unit displays an error code. Using this Rinnai tankless water heater error code guide, you can quickly determine what the problem is and if you need a plumber to service the unit or if you can fix it yourself.

Rinnai Error Code 02: No burner operation during freeze protection mode

Call a plumber.

Rinnai Error Code 03: Power interruption during bath fill

Turn off all hot water faucets/taps. Press On/Off button twice. Turn hot water back on and test. You may have to try this a couple times to reset the system.

Rinnai Error Code 10: Exhaust or air supply blocked

There are several things you can do before calling a plumber. Try the following:

• Check venting material. Is it Rinnai-approved? (See Rinnia-approved venting materials here.) If not, replace venting material or have a plumber replace it.
• Look for blockages in both the flue inlet or exhaust.
• Are the venting components properly connected?
• Check the condensation collar. Is it loose or improperly installed?
• Are the dip switches set correctly?
• Is the fan rotating properly, or is something blocking it?
• If the error code still shows, call a plumber.

Rinnai Error Code 11: Ignition problems

Because this has to do with gas and gas lines, most people will need to call a plumber to handle this. However, these are steps the plumber will take (and you could carefully try some of these yourself):

• Is the gas on? Check at the water heater, gas meter or cylinder.
• Is the gas type and pressure correct?
• Is the gas line, meter and/or regulator sized properly?
• Is the air in the gas line? Have a plumber bleed the air from the lines.
• Are the dip switches set?
• Is the appliance grounded?
• Disconnect EZConnect™ or MSA controls to see if you can isolate the problem.
• Does the igniter work? Is it operational or do you need to replace the igniter? Check the wiring harness and see if it’s the igniter or the harness.
• Examine the gas solenoid valves. Any open or short circuits?
• Remove the burner cover and examine the burners to see if they are one, properly sealed, and two, if the burner surface has condensation or debris on it.
• If you are not familiar with these parts and with both wiring and gas, you should hire a plumber to deal with a Rinnai error code 11.

Rinnai Error Code 12: Flame failure

Because this has to do with gas and gas lines, most people will need to call a plumber to handle this. However, you could carefully try some of the steps a plumber will take. Use the checklist for Rinnai error code 11 (above), and if those steps don’t fix the problem, try the following:

• Check power supply. Any loose connections?
• What is the voltage? Any voltage drops?
• Is the flame rod wire connected? Any problems with carbon build up on the flame rod?
• Check for DC shorts at components.
• If you are not familiar with these parts and with both wiring and gas, you should hire a plumber to deal with a Rinnai error code 12.

Rinnai Error Code 14: Thermal fuse

Something is wrong with the thermal fuse. You may be able to fix it by trying the following:

• Check for air flow restrictions.
• Is water flow in the circulating system low? This can cause problems related to short-cycling.
• Check dip switches.
• Anything gunking up the combustion chamber? What about the exhaust pipe? Obstructions can cause problems with thermal fuse function.
• How does the heat exchanger look? Any cracking or separations? Hot spots? Hot spots indicate scale build up.
• Flush the heat exchanger following the instructions on the owner’s manual.
• Check the resistance of the safety circuit.

Rinnai Error Code 16: Over temperature warming

This problem usually is caused by a restriction of airflow. Check for clogs or obstructions in the following:

• Combustion chamber
• Exhaust piping
• Heat exchanger

You will also want to check for restrictions in air flow around unit and vent terminal and for low water flow in a circulating system causing short-cycling. Once you clear the obstructions and improve airflow and water flow, the problem should resolve itself. If it does not, call a plumber.

Rinnai Error Code 32: Outgoing Water Temperature Sensor Fault

This one is simple: carefully examine the sensor. Look for damage and scale build up. You probably have to replace the sensor if cleaning it doesn’t help.

Rinnai Error Code 33: Heat Exchanger Outgoing Temperature Sensor Fault

Similar to above. Carefully examine the sensor. Look for damage and scale build up and make sure the fan blade is tight on motor shaft and is undamaged. You probably have to replace the sensor if cleaning it doesn’t help.

Rinnai Error Code 34: Combustion Air Temperature Sensor Fault

Same as above. Carefully examine the sensor and wiring. Look for damage and scale build up. You probably have to replace the sensor if cleaning it doesn’t help.

Rinnai Error Code 52: Modulating Solenoid Valve Signal Abnormal

You probably need to replace the solenoid valve. First:

• Check modulating gas solenoid valve wiring harness for loose or damaged terminals.
• Measure resistance of valve coil.
• You may be able to resolve the problem by tightening loose terminals.

Rinnai Error Code 61: Combustion Fan Failure

Examine the combustion fan to see:

• Can the fan turn freely?
• Any problems with the wiring harness? Maybe it has been damaged or has loose connections?
• Is there a problem with the motor winding resistance?

Rinnai Error Code 65: Water Flow Control Fault

You definitely need to call a plumber for this one. The water flow control valve has failed to close during the bath fill function. Immediately turn off the water and discontinue the bath fill function. Then call a plumber.

Rinnai Error Code 71: Solenoid Valve Circuit Fault

You probably need to replace the solenoid valve. First:

• Check wiring harness to all solenoids.
• Measure resistance of each solenoid valve coil.

Rinnai Error Code 72: Flame Sensing Device Fault

Before you call a plumber, you can try the following:

• Check to see if the flame rod is touching flame when the unit fires.
• Examine the wiring to flame rod for damage.
• Clean the flame rod with sandpaper.
• Examine inside the burner chamber for debris or gunk that might be blocking the flame at the flame rod.
• Replace flame rod.

Rinnai Error Code 00 or “LC”: Scale build up in heat exchanger.

Call a plumber and have them flush the heat exchanger or replace the heat exchanger.

Note: A lot of customers ignore this code because it still allows the tankless water heater to continue running. You will see the display alternates between the LC code and the temperature setting. Make sure you get the heat exchanger serviced and don’t ignore this code just because it allows you to still run the unit or you may have more serious problems down the line.

Rheem Tankless Water Heater Error Codes

Rheem tankless water heaters are a solid choice anytime. The self diagnostic tools make it easy to quickly identify what is wrong and how to fix the system. Use this Rheem error code troubleshooting primer to determine what’s happening with your water heater.

Rheem Error Code 00

Indicates 1-hour continuous combustion. To correct this code, close all hot water taps to reset the unit. Turn off or remove circulation pumps.

Rheem Error Code 05

Indicates imperfect combustion. To remedy the problem, clean the air inlet filter, air fan and exchanger fins. Check that the air ventilation openings are open and clean, if necessary.

Rheem Error Code 10

This is the false flame detection code. Before calling for service, check to make sure that nothing is blocking the flue inlet or exhaust.

Rheem Error Code 11

No ignition. Check to make sure there is gas to the unit and that the pressure is correct. Ensure the ignitor is operational before calling for service.

Rheem Error Code 16

This is an over temperature warning which could indicate a possible clogged heat exchanger. There may also be restricted air flow around the unit. Call for service.

Rheem Error Code 29

This code indicates that the heat exchanger outlet temperature is too low. By cleaning the heat exchanger air inlet, the problem is typically resolved.

Noritz Tankless Water Heater Error Codes

Noritz Error Code 11
This indicates ignition failure in your tankless water heater. It means that your unit is not firing up to heat the water, a situation that can be caused by insufficient gas supply, insufficient airflow or debris on the ignition plug.

After checking to see if the gas is turned on, call a plumber. He or she will make sure your gas valve is open, the exhaust vent is unobstructed and the ignition plug is firmly attached and free of debris.

Noritz Error Code 12
A code 12 means the unit has a weak flame and that water is not being heated properly. Similar to a code 11, this is caused by lack of gas or airflow.

Call a plumber who will likely take similar steps as outlined for code 11.

Noritz Error Code 16
A sharp spike in outlet water temperature will cause a code 16. This often results from scale buildup, which hampers heat-transfer efficiency and makes the unit try to compensate by burning hotter.

Since this error can be caused by scale buildup or hard water, performing a descaling procedure or using a water softener may resolve it. Contact a plumber to make sure this is the case.

Noritz Error Code 29
This code indicates a problem with condensate drainage. In condensing tankless water heaters, a special drain line equipped with a neutralizer (to reduce the acidity of the outflow) removes the condensate. A blockage in the condensate drain line or incorrect condensate drain piping would cause the burner to flood if not for this error code.

Call a plumber, and he or she will check to make sure the condensate drain line is properly routed and unobstructed.

Noritz Error Code 73
Improper circuit board settings will cause a code 73 error. Changing a jumper connection or dip switch while power is supplied to the heater can trigger the problem, as can an improperly programmed circuit board.

Unplug the heater for 30 seconds and then plug it back in. If the error code persists, call a plumber.

Noritz Error Code F76
This error code involves a breakdown in communication between two tankless water heaters using the Quick Connect Cord. It can occur when more than one remote is hooked up to handle two Quick-Connected units.

Make sure that only one remote control is hooked up when two units are connected. If the error continues, contact a plumber.

Noritz Error Code 90
A code 90 indicates a combustion abnormality caused by an improper mixture of air and fuel. Possible culprits are insufficient gas supply, a blockage in the fuel vent or debris in the fan motor.

You will need a plumber to resolve this error. He or she will check gas pressures, venting length, dip switches, etc.

Bosch Tankless Water Heater Error Codes

Bosch Error Code 11

Indicates a problem with the tankless water heater’s ignition. Typically, if you receive this fault code, your unit will not work. Before calling a licensed plumber, check to make sure your gas valve is open and supplying gas to the unit.

Bosch Error Code 29

Indicates a possible clog in the unit’s neutralizer. To correct this problem, it requires a qualified plumber.

Bosch Error Code 90

Indicates low gas supply pressure. To remove the code, turn the remote control unit off and turn on the hot water tap. Then, press the ‘on’ button on the water temperature controller again. If the fault code remains, you will need to call for service.

Bosch Error Code 92

This typically means that the water heater’s neutralizer will need to be replaced soon. You can continue to run your hot water heater with fault code 92, but the flow of hot water will be reduced. Call for service to replace this part.

Bosch Error Code 99

Indicates an abnormal combustion. Your water heater will shut down if this code appears as a safety precaution. Don’t attempt to light the burner within the unit by hand. Call for service.

Need a Charlotte Tankless Water Heater Expert?

If your Charlotte area tankless water heater is in need of service, give us a call at 704.846.5371 for fast and expert service. Open 24/7, and never an extra charge, not even for evening, weekend or holiday tankless water heater service.