Vaillant Authorized Service Unable to Explain Boiler Issues

About 2 years ago, we decided to install 3 Vaillant brand combi boilers for the central system heating installation in our building. Installation was completed without any problems. Except for minor problems, we have been using it for 2 years without any problems. About 2 weeks ago, Kastamonu Vaillant Authorized service, who came for routine maintenance, reported that the main cards of two of our 3 combi boilers, which worked throughout the winter and were turned off up to the fuse switch with the end of the winter season, were burnt. To summarize, why/how? When we asked why it could have happened, the service representative made different explanations, and the dealer who made the initial installation made different explanations. The service representative said that even if we send the parts for warranty, they would probably not be covered by the warranty. As a result, we demand from Vaillant the solution to our problem with these products, which we decided and purchased by taking the brand-company reliability as a measure. Thank you.