A high efficiency water heater does not have a lot of moving parts. Nonetheless, it does require periodic maintenance to operate properly and avoid a costly, catastrophic failure. Depending on the brand purchased different items may need to be checked. However, it is a safe bet that basic steps like inspecting intake and exhaust screens for blockage,checking and cleaning float switches, giving the combustion chamber a visual check, looking for leaks and taking readings of critical date will be universal. Lack of performing these basic steps may result in damage to the heat exchanger ( Big money) or the combustion chamber. If you don’t feel comfortable doing the PM, call a qualified service company like Yankee to do the work. It is a small annual investment that will pay big dividends.