the engineer was actually really good and managed to keep the condensing pipes inside the utility room, very tidy, too, so they don't freeze in the winter, I can't fault him really, he tried his best.
That is actually quite a big problem with a lot of new condensing boilers that have been fitted, so glad he went to the trouble. It may be you do just have a pig of a system that gets a bit grumpy now and again, these problems sometimes sort themselves out.
As for the DW & WM any air in the pipes could be released by just running the taps near to the appliances seeing as they are connected just under these taps. Seeing as it is a new boiler, the plumber may have altered the pipe work and as such may not have flushed the pipes, flux used to make alterations can cause flaking, these flakes then travel round your system and get stuck in filters. On both your DW & WM disconnect the flexible pipes and check the small gauze filters on the end of the flexible pipes, you may find small green flakes that are resricting the flow to the appliances