we have had this on more than once from vaillant same engineers? water spotless also when their engineers have booked replacing certain parts and we found the new part in rubbish their engineer through in customers bin but they took back out as soon as the engineer left so no more installs from us with any vaillant or glow worm boilers for the last 3 years. we have no problem with Worcester bosch so will stick with them
Ye fair play to Worcester they are pretty good. I went to a job after a Worcester engineer and the customer said that the heat exchanger was blocked with sludge but Worcester still replaced it free of charge and said that they wouldn't replace it again if it's due to sludge and that they need a power flush! Fair play to them!