my combi80 has just stopped running!?

my potterton combi80 now called a baxi potterton combi80 stopped running at 4 o'clock the other day, there was no noise at this however this is the time it's clock stopped, the boiler's mains light is no longer on, i've checked the plug fuse and changed it but this hasn't worked, what else can i do? it's the boiler i've inherited in my first flat so i don't have a user manual to run any further checks before having to call an engineer which could prove expensive.