Myson Apollo boiler - fuse keeps blowing?

Hi

I have a Myson Apollo boiler.

The electricity supply to the electronic heating controls has blown the fuse. I replaced the fuse and it blew again straight away.

There doesn't seem to be a problem with the electronic heating controls themselves as they are still running on the battery backup but won't active the boiler.

Does anyone know what might be causing this to happen. I think there must be a problem with some part of the heating system eg. the fan on the boiler or the pump but not sure where to start.

Any suggestions much appreciated.