Yeh fair enough steelmasons (y), I was just saying what I got told on a Vaillant installer Corse but I think that was more for commisioning, I didn't want to give any numbers and values as it was my first post and not sure on the rules on giving out advice on gas related problems :D
all its done is adjust the heat output I would of thought it should still be treated as a 438, I thought you only had to check the maximum setting on a Vaillant because they say it should work safely across the range if the maximum setting is correct