Vaillant Combi Boiler Keeps Shutting Off and Service Only Says Filter Is Full

We have been using our Vaillant combi boiler for about two years, but it consistently shuts off intermittently and goes into protection mode. Each time we call for service, the authorized technicians simply state that the boiler’s filter is full and leave without taking further action. Despite having the combi boiler and radiators cleaned several times, the issue persists. After each service visit, the boiler resumes cutting off the flame and going into protection mode shortly afterward. Today, November 5, 2024, the service personnel came and, once again, stated the filter was full and advised us to clean the radiators, even though we had them cleaned just last week. No other action was taken. We urge Vaillant to address this ongoing heating issue with the necessary attention, as it has been affecting us for two years now.