I have had an issue with the boiler from day one. It makes a loud clicking noise at random times throughout the day and night. It has been loud enough to wake me up (and I sleep in the room above it’s location). A Viessmann engineer has attended three times in the last nine months and failed to diagnose the fault, it has still not been fixed. I sent an email to Viessmann two weeks ago to ask for the engineer to re-attend and fit the parts he ordered a month ago, but they have failed to reply to me. I’m at the point of rejecting the boiler due to the unsatisfactory loud clicking noise it makes. I will buy Worcester Bosch next time as I’ve never had any issue with their boilers.