Gtbarringer I think probably an SSR inside the Gicar box failed on (as SSRs usually do). Presumably Stean boiler SRR This means both boilers were capable of being on at the same time, the machine trying to draw a lot of power (as you had just switched it on). This would be in excess of 20 amps and caused the problems below.
You will need a new power socket, some new cable ends crimped on, and a Gicar box, unless you have soldering skillz to replace the failed SSR.
That’s my best guess anyway.