you have an electrical fault. The fuses are attempting to protect your appliance. If you keep replacing the fuses without identifying and correcting the fault, you will do more and more damage.
Not being a boilerman, if it was me I would start by looking for a water leak dripping onto an electrical part, perhaps around the pump or a motorised valve if you have one, which you might be able to fix with a simple plumbing repair, or around the cylinder thermostat. As an inexperienced amateur you should not be taking a gas boiler apart. You can also look for obvious damage to the cables, such as rodents (as above) or a heavy object crushing flex.
If you insist on powering up the boiler when you already have a fault you might damage the electronics, which will be an additional expensive repair on top of whatever fault you already have.