There is nothing wrong with guessing - just as you guess the 3A fuse is the cause of your boiler not firing up my guess is that it is NOT the cause.
Fuses are safety devices to protect wiring and equipment from damage in the event of a fault. If a fuse blows it is usually because something went wrong and caused the fuse to blow.
Your 3A fuse may indeed have blown (but I doubt it) but a new 3A fuse will still be subject to the fault that caused the original fuse to pop.
Boilers often have a 1A fuse inside to protect the control electronics.
Your boiler will have a wall mounted switch box nearby with a neon indicator and a removeable fuse link often held in with a small screw - undo the screw to remove the fuse holder. If the neon light is on then the fuse is good and will not need to be tested or replaced - if the neon light is off then your original guess was correct.
Good luck...
Peccavi, May 2010
