Have you ever had your hot water cut out and noticed Error 10 flashing on your Rinnai RL-75 tankless water heater? This is a diagnostic code that basically means the unit is starved for air or is struggling to expel exhaust.

If this happens just once in a great while, simply restarting your heater will usually suffice to get things running again. However, if it starts happening often, or your hot water suddenly goes freezing cold while you are taking a shower, you definitely need to address it.

What causes Error 10? The usual reason is that the internal ventilator fan (blower motor) or the air vent desperately needs cleaning. Over time, the fan cage acts like a vacuum and gets completely packed with dead bugs, dust, and insect debris, which blocks the airflow.

How to fix it: Asking a plumber to come out and service a tankless heater can get really expensive. But, if you are a “do-it-yourselfer,” it is entirely possible to fix this yourself! The process involves safely shutting off the power/gas, removing the front heater cover, pulling out the ventilator fan, and cleaning all the bugs out of the fins.

Newer Rinnai heaters now have a filter screen that you just pull out and clean the bugs easily, but my home built in late 2020 has an older RL-75 version that lacks the filter so the bugs get trapped inside the heater’s fan.

You definitely shouldn’t attempt this without clear instructions. I used Google’s free Gemini AI to give me instructions, and it recommended an excellent step-by-step YouTube video that let me fix the heater myself. Click to watch it:

• FIX Error CODE 10, RINNAI RL75, REMOVE DIRTY FAN TO CLEAN (This one perfectly matched my exact unit and shows exactly how much bug debris gets trapped inside!)

Hopefully, this saves some of you a cold shower and a plumbing bill!
You can also save if you read my other article:
Save $400+ Yearly: Flush Your Water Heater Yourself
Once a year you have to flush your heater with vinegar or it will stop working, and you can do it yourself and avoid a $200-400 bill.