How can i fix my combi boiler/ central heating (make is Potterton Lynx)?

Hi When i switch on my boiler it starts up for a minute or so then trips the switch off in the fuse box. This stops any electrics working on the ground floor, which will only work if i switch off boiler and put the switch on in the fuse box. I have tried changing the fuse in the plug of the boiler and i have also tested the sockets of where the boiler plugs in using my kettle but it still happens leaving me with no heating in the house or hot water. Why is this happening and how can i fix it without having a whole new boiler installed.

Thanks.