Harvey Lewis at Certified Plumbing did a fabulous job repairing our leaking tankless Noritz unit. All other plumbers wanted to just replace the entire unit, but Harvey worked with us to replace the leaking heat exchange. This meant taking the entire thing apart, replacing that part and then putting it all back together! It was a huge job that took and entire day....but he was super thorough, patient and did a great job! The next day we got error messages and no hot water. I was thinking we were going to end up having to replace the whole thing. But Harvey came back out and spent half a day trouble-shooting and found that there was a blockage in a line that was restricting the water flow out of the unit..causing it to shut down. Would never have guessed water flow would be the reason. Once line was cleared, we have been good ever since! He even swept my attic once he was done! Actually left it cleaner than when he started!!!
I HIGHLY recommend him for working on your tankless heater!!