Oh, sorry, The Trician, I didnt seee your reply until after I wrote that last comment.
The manual says "if the blue light flashes your boiler has a fault" duh! It says to ring an installer to find out what they mean, but it's 10pm and I have no credit on my phone.
I've fixed it for now, and will send hubby to lag the pipe properly tomorrow, we're supposedly having snow all week, so don't want it freezing again!
Thanks for replying