Honestly, the UK support is dreadful. And we are still in warranty. In 5 years since install we have had multiple "recommended" engineers come out to try to fix the same fault, all of whom gouged very heavily with their bills and were never again to be contacted. I would strongly recommend steering clear of Viessman, as the recommended support guys are unable to fix the hardware and, of course, they are not employed by Viessman so not their problem. The Viessman people in head office are friendly. But the problems I have had would make me very reluctant to ever go back to Viessman. Avoid if you can.