I think I should update the thread on the latest update , BG contacted me to make sure I was happy with everything and I subtly mentioned in conversation that one engineer had thought the boiler was small for the job. They arranged for a a Heat survey to be done which came out at a score of 29. It has taken them 4 weeks since but I have just had confirmation that they will be replacing the boiler free of charge to to the CDI 30 Greenstar. I am one happy customer . Many thanks to all those that helped with advice in the thread!