Replacement parts designed specifically for Bosch AquaStar water heaters can generally be used to fix a faulty unit. Like many tankless water heaters, Bosch AquaStar water heaters use a number of proprietary parts.
Traditional water heaters often use standard fixtures and other parts, so experts might be able to use non-branded replacement parts. Tankless water heaters, on the other hand, are built to be portable and as efficient as possible, so branded parts designed for specific models are frequently used. Fortunately, some of the small items that break on tankless water heaters are relatively inexpensive even if they're branded, especially when compared to the cost of labor.