I had this problem, worth noting that from the startsmart first page you have options for CD/DVD or just DVD, dont know why but it only works from the DVD only option.
I dont think myself clever at all, but it doesnt really say much for Corgi accreditation either does it? as with all of these so called industry recognised papers at the end of the day its pure luck if you get someone that knows their stuff, and yes he charged me £30 for the call out.
Just thought Id post this as it may help others.
Boiler started playing up a few weeks ago, occasionally it would go into lockout, sometimes on CH mode sometimes on DHW mode but especially if the boiler was running in CH mode and you then went to run the HW.
Steadily got worse until one day...