Vaillant Wireless Room Thermostat Not Working

Hello, my Vaillant brand boiler, model 376/5, has exceeded my expectations. The wireless thermostat, on the other hand, has left me very unhappy. Since the beginning, I have repeatedly reported my issue to customer service representatives. I programmed the thermostat, but during power outages, it updates itself to January 1, 2010, at 00:00, causing the hourly programs to change. After each outage, I must manually intervene in order for the programs to function properly. When I'm not at home, the programs behave differently depending on the time. I've mentioned this issue at each maintenance visit, and while they inspect the thermostat, the problem remains unresolved, becoming apparent during the winter. I was even advised to replace the battery as a possible solution, but this did not work. Finally, I made resolving the thermostat issue a requirement for extending the warranty. The customer service representative assured me that it would be resolved and made a note of it for the maintenance team. The maintenance team, on the other hand, acknowledged the issue with these models and attempted to sell me a new thermostat. I want to believe in Vaillant, a company I trust, to find a solution to my three-year ordeal and keep their promise to resolve the issue for warranty extension.