Seriously, I could kiss you! Mate I don't know how I didn't try that before but it just worked - you've saved me £200 and a whole lot of grief off the missus for wasting money!
I shut it all down took the batteries out, fired it up, pressed/held button 1, pressed button 2 - quick Red LED flash then went out for the first time.
Put the batteries in and hey presto. Boiler fired!