Hi! I worked with a local plumber to install a new tankless water heater (Rinnai Sensei RX119iN) but whenever the burner turns on, there's a very loud vibration for around 1.5 seconds, then a pause for around 1-2 seconds, then another vibration. Occasionally it would error with error code 12. We initially had a 1/2 inch gas pipe, so we just upgraded to a 3/4 inch gas pipe less than 30 feet away from the gas meter. But we're still running into this issue of vibrations and the occasional error code 12.

Very lost at what else we could try... Anyone have any suggestions?

Has a gas pressure test been performed before and during the burner turning on?

No gas pressure test but I'm expecting the 3/4 inch gas pipe to have been enough since it came directly (<30 feet) from a meter rated for 250 CFH


I found a local professional through Rinnai's website and he said
1. The vibrations are caused by having too much water pressure (pressure reduce valve needed replacement, Water pressure is at 100 psi) and the water pressure entering the house not matching the pressure entering the tank. He recommended replacing the pressure reduce valve and adding a thermal expansion tank on the cold water line into the tank. Something like [www.homedepot.com]
2. Error code 12 is caused by an insufficient outtake vent. We have it going up from the heater a foot or so then slanted at around a 45 degree angle outside through a wall. He said it needs to go straight up because tankless heaters get so hot. Since we have a second floor right above where it's currently installed, he said we'd need to move it outside. However it seems like Rinnai has products like this for "SE+ and SE Series Tankless Water Heaters", Not sure if mine falls into that category, but these clearly are not going straight up and look like can be used in my case to vent air out with a Rinnai provided solution. Do I really need to vent air straight up for the Rinnai Sensei RX119iN? [www.homedepot.com]


Any thoughts on the above? Definitely going to fix the pressure reduce valve but I'm doubting if I really need to move it all outside. And I do have a solution for the outtake air currently. He was saying it's not adequate and would melt but regardless, would that really cause error code 12?

Do you have the troubleshooting guide for the heater?

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