I'd been experiencing some problems with a Viessman gas boiler and, after a visit from the manufacturers engineer, some recommendations were made relating to the system. I looked on line for a Viessman trained engineer and found Stephen. He arrived when he said he would. I was happy to accept a reasonable verbal quote from him and he carried out the work within a week or two. Sadly, one of the modifications didn't quite work as it should but it was a month or two before I noticed it. Stephen came, made recommendations which, sadly, didn't solve the problem. My solution would have been to replace the malfunctioning part but this quiet man is a thinker; he dug deeper, and came up with the solution. I feel my boiler will be in safe hands from now on.