There is minimal maintenance to keep the water heater running good as new. Here is a quick link to some helpful steps http://www.wikihow.com/Maintain-a-Tankless-Water-Heater
I'd expect that you have a warranty longer than just 30 days. Probably at least 1 year, right? I'll base my answer on that premise.
In the first 30 days, you should look for things that are incomplete ... read more