Rinnai Tankless Water Heater Code 10 – Fixed

There’s nothing worse than an involuntary cold shower, but the real pain comes when you need to figure out what the error code in your Rinnai tankless water heater means and how to fix the issue. So, what does Rinnai tankless water heater code 10 mean? 

Rinnai tankless water heater code 10 means that there is an overheating issue. This is usually due to a blockage in the venting system, which can be caused by lint, debris, or even animals nesting in the vents. Other causes include a defective sensor, incorrect gas pressure, or a stuck check valve.

This article discusses everything you need to know about Rinnai tankless water heater code 10. We’ll explain what it means, what causes it, and how you can fix it. Let’s get started! 

Rinnai tankless water heater

1. Obstruction in the Venting System

Your Rinnai tankless water heater needs adequate airflow to function properly, and this is especially true for gas-powered models. The venting system helps to regulate the temperature and prevent the unit from overheating.

When the venting system is blocked, it’s likely to cause error code 10. This can be caused by various things, including dust, lint, or nesting critters. However, the good news is that this is easy to fix.

How To Fix

Simply clean out the fan and vent to eliminate the code 10 error. You can use a vacuum cleaner with a hose to reach into the ducts, but be careful not to damage the unit while cleaning it, though.

If there’s an animal nest in the vents, you’ll need to remove it carefully. Once the nest is gone, the code 10 error should go away. If you don’t feel comfortable doing this yourself, you may need to call a pest control specialist to do the job and attend to any critter issue you may have. 

2. Defective Sensor

Sometimes, the code 10 error may be caused by a defective sensor. However, this is more common in older Rinnai tankless water heater models. 

After determining that it is a sensor issue, you will need to replace it. 


How To Fix

If you suspect that your water heater has sensor problems, your best bet is to call a professional. They can figure out what’s happening and replace the sensor if necessary.

You can also order a new heat sensor online and replace it yourself. However, this can be a complex process if you’ve never done it before. I would not recommend it unless you’re very confident in your ability.

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3. Incorrect Gas Pressure

Another possible cause of code 10 on your Rinnai tankless water heater is incorrect gas pressure. The unit needs a certain amount of gas pressure to function correctly, and if the pressure is too high, it can cause overheating and a code 10 error to appear. 

The telltale sign of incorrect gas pressure is a hissing sound from the unit. If you hear this, turn off the unit immediately and call a professional. However, incorrect gas pressure will not always be as noticeable, and you will sometimes only get the Code 10 error.

How To Fix

If you feel confident about checking the gas pressure in your water heater, start with the gas pressure regulator, and make sure it is set to the correct pressure. Most Rinnai models require a gas pressure of 7 inches Water Column (1.74 kPa), so that’s what you should be aiming for. 

Alternatively, can a technician if you don’t feel comfortable with this, or if the pressure seems off. They should be able to fix the problem quickly and get your unit back up and running again.

4. Stuck Check Valve

A stuck check valve can also cause error code 10. This valve is designed to keep the water from returning to the unit. If it gets stuck in the wrong position, it can cause problems.

The most common symptom of a stuck check valve is no hot water. If you turn on the unit and there’s no hot water, this is a good sign that the check valve is stuck.

stuck check valve

How To Fix

Luckily, this one is pretty easy. All you have to do is turn off the water supply to the unit. Then, open up the access panel and locate the check valve. With a pair of pliers, loosen it up and get it moving again.

If the valve is indeed stuck, you may need to replace it. This is a pretty easy fix that most people can do themselves. Otherwise, have a technician do it for you. 


There you have it! These are some of the most common causes of a Rinnai tankless water heater Code 10. If you’re getting this error, don’t worry. In most cases, you can deal with the issue yourself.

However, if you’re not confident about DIYing your Rinnai tankless water heater, call a professional.