I purchased a Takagi tankless water heater that Donovan Jorgenson in Milwaukee, WI installed. After 4 years of operation, it started making rumbling noises whenever it tried to turn on. I called the plumber that Donovan Jorgenson contracted with and he flushed it out with a vinegar and water solution. It still wouldn't work. Then I had the burner cleaned. It still wouldn't work. Then I got only the first name (Robert) of the company representative in Chicago and he promised to come and work on it. After a few phone calls back and forth to set up a time, he began to refuse to take my phone calls. The people in California were useless and refused to help out as well.
Now I have a useless piece of junk hanging on the wall of my basement. It was still under warranty when the problems started. I paid over $3,000 for this tankless water heater. I went back to a conventional water heater because I needed one that worked. Takagi just washed their hands of my water heater problems. I contacted the Better Business Bureau but nothing was accomplished by doing that.