Rinnai Tankless Water Heater: Troubleshooting and Code Diagnosis Guide

Rinnai’s tankless water heaters are known for their efficiency and reliability, with the brand being renowned for its residential and commercial-grade tankless water heaters with the industry’s best warranty. However just like any appliance, even Rinnai’s vaunted water heaters can occasionally experience issues. 

This guide provides a step-by-step approach to troubleshooting common problems, understanding diagnostic codes, and resolving issues in Rinnai’s tankless water heaters.

Common Issues with Rinnai Tankless Water Heaters

1. No Hot Water

Possible Causes:

• Insufficient gas supply or a closed valve
• Tripped breaker or power supply issue
• Clogged water filter or scale buildup

Solutions:

• Check and open the gas valves.
• Reset the breakers, or check for power at the unit.
• Clean the water filter and descale the heater if necessary.

2. Water Temperature Fluctuates 

Possible Causes:

• The water demand exceeds the water heater’s capacity
• Incorrect temperature settings
• Scale buildup in the heat exchanger

Solutions:

• Reduce simultaneous water usage. If it persists, you may need to upgrade to a unit with a larger demand capacity.
• Adjust the temperature settings.
• Descale the heat exchanger.

3. Heater Won’t Turn On

Possible Causes:

• Power supply disruption
• Faulty ignition system

Solutions:

• Verify the unit is plugged in and has power.
• Check the diagnostic code for further troubleshooting.

4. Error Codes Displayed

In the event of an issue, Rinnai’s tankless water heaters display diagnostic codes, which provide specific information about the problem. Refer to the table below for solutions.

Rinnai Diagnostic Codes and Troubleshooting

Code	Issue	Troubleshooting Steps
02	No burner operation during freeze protection.	Ensure gas and power are supplied to the unit. Check for frozen pipes.
10	Air supply or exhaust blockage.	Inspect venting for obstructions or improper installation.
11	Ignition failure.	Check gas supply and ignition components. Reset the unit and try again.
12	Flame failure.	Verify proper gas flow and ensure the flame rod is clean.
14	Thermal fuse issue.	Check for overheating or blocked heat exchanger. Replace the fuse if necessary.
16	Over temperature warning.	Reduce water temperature setting and inspect for scale buildup.
19	Electrical grounding issue.	Ensure proper grounding of the unit. Consult an electrician if needed.
25	Condensate trap issue.	Clean the condensate drain line and trap.
32	Outgoing water temperature sensor fault.	Inspect the temperature sensor for damage or loose connections. Replace if faulty.
33	Heat exchanger outlet sensor fault.	Similar to Code 32: inspect and replace if necessary.
52	Modulating solenoid valve fault.	Test the valve operation. Replace if it does not respond.
61	Combustion fan fault.	Check the fan for debris or damage. Replace if it fails to operate.
71	Solenoid valve circuit issue.	Inspect the valve circuit for continuity and repair or replace if necessary.
99	System error.	Perform a full system reset. If the issue persists, contact Rinnai support.

Note that these table applies to most of Rinnai’s tankless water heater units sold by Total Home Supply.com. Some models may have their own specific codes that are included in this table.

For the complete list of diagnostic codes, refer to Rinnai’s TWH Troubleshooting.

Rinnai Tankless Heater Maintenance 

☑ Descaling and Cleaning

• Regularly descale your unit to prevent mineral buildup. This should be done at least once per year.
• Clean the water inlet filter to maintain flow.

☑ Inspect Venting

Ensure vent pipes are free of obstructions and properly installed.

☑ Check for Leaks

Inspect all connections for water or gas leaks and tighten or repair as needed.

☑ Annual Professional Maintenance

Schedule a professional inspection annually to ensure peak performance and address hidden issues.

When to Call a Professional

Not all issues can be solved by the user. Contact a certified technician in case if you encounter the following:

• Persistent error codes that do not resolve after troubleshooting.
• Gas-related issues or leaks.
• Complex electrical faults or system failures.

By following this guide and addressing issues promptly, you can ensure your Rinnai tankless water heater remains reliable and efficient for years to come. And if it’s time to replace your well-worn unit, we carry a wide range of Rinnai hot water heaters.

You may also be interested in these related articles:

General Hot Water Heater Troubleshooting

Water Heater Replacement Guide