Have you ever been in the middle of a shower only to have the water go freezing cold? If you check your Rinnai tankless water heater and see Error 10 flashing on the display, you aren’t alone.

What is Error 10?

It’s a diagnostic code indicating that the unit is “starved for air.” It is struggling to either pull in fresh air for combustion or expel exhaust.

If this happens once in a blue moon, a simple restart usually does the trick. However, if it becomes a regular occurrence—or you notice a loud humming sound coming from the unit—it’s time for a deeper look.

The Culprit: Bugs!

The most common cause of Error 10 is a dirty internal combustion fan. Over time, the fan blades become caked with dead bugs or dust. Because these blades are finely balanced, even a small amount of debris can cause the fan to wobble, hum loudly, and eventually trigger the error code.

While newer Rinnai models feature a built-in filter screen for easy cleaning, many units installed circa 2020 (like my RL-75) lack this filter, allowing debris to get trapped directly inside the blower fan.

Can You Fix It Yourself?

Calling a plumber can be expensive. If you are comfortable with basic tools, this is a very manageable DIY project. The process involves:

1. Safely shutting off power and gas.
2. Removing the front cover.
3. Pulling out the ventilator fan.
4. Cleaning the debris out of the fan fins.

Resources to Get You Started

I used Google’s Gemini AI to find the best instructions, which led me to this excellent step-by-step tutorial. This video features my exact RL-75 unit but can apply to other older models. It shows just how much debris can get trapped inside. The second video from Rinnai is less detailed but also helpful.

• Primary Guide: Fix Error Code 10, Rinnai RL75, Remove Dirty Fan To Clean
• Rinnai Official Maintenance Video

Pro Tip for the Motor: When you’re ready to remove the motor, look for it’s own wiring clip. To detach it, press down firmly with your thumb on the shortest part of the connector; the two pieces should slide apart easily.

Tip When Cleaning: After you remove the fan motor to clean, before reinstalling, first press a leaf blower against the vent hole in the back of the heater to blow any debris in the exhaust pipe out through the outside vent. A shop vac also works if you reverse the hose to blow air instead of sucking it.