Over time, you gain a lot of experience. There are numerous companies with whom we enjoy working and sharing expertise, or whose products we like to use because of their good quality. But at this point, we can't list all the companies whose products we really like, or with whom we have worked hand in hand on several occasions. There are simply too many.
It also doesn't make sense to single out individual companies and list them here, because your plumbing installer is most likely good too - we generally like to work with companies that have been servicing our customers' systems for years and are willing to work with us as well.
They know the system, we tell them what settings we'd like to have—e.g., temperature control, taking into account the switching hysteresis and the control settings for the charging pump—and then we look at how best to achieve this with the existing control system.
Especially during inspections, it is sensible for the plumber or the caretaker or a committed and capable owner to come by from time to time, which we are generally unable to do at a reasonable cost-benefit ratio due to the significantly longer travel distance.
Plumbers aren't incompetent because we're now coming "on board," but our expertise complements each other, and we get to know the property from a different perspective, thanks to our different approach. Consequently, we identify problems, weak points, or even errors that were previously overlooked; otherwise, there would be no reason to do so. At the very latest after initial training, we have a 3D representation of a drinking water installation for an expert report. Plumbers don't normally need to familiarize themselves with a system in this way. They're called when something needs to be repaired or installed. Sometimes, however, it's also difficult because, as a customer, you can't judge whether the plumber is trying to make money or whether, for example, the storage tank actually needs to be replaced... An independent expert is a solution that is usually a practical solution for the plumber and the homeowner's association or the property owner, eliminating this "mistrust issue" and instead providing clear opinions.
At this point, it's important to emphasize that it's our job to find and solve errors and problems; everyone benefits from this, or at least that's how the companies that work with us see it.