carter840 Service boiler is steam boiler yes.
testing an SSR which is an opto coupled device really needs to be done with an appropriate load in a test rig and they do need to have an in range load attached to them. You can see them with the cover off and trace which boilers they power.
There is a simpler way for you…its unreasonable to think both SSRs would have failed simultaneously, unless there was a lightning strike or something. So pull the terminals of the service boiler heating elements (isolate them well, so you don’t get magic blue smoke) and let the brew boiler heat up and then switch on and off normally.
If it does (and I think it will)…switch off, unplug machine, remove the service boiler SSR and replace it with the brew boiler SSR, don’t bother putting the old SSR back in the brew boiler bit. Just make sure the wires can’t short, cos of the blue smoke.
Switch on and see if the service boiler can be switched on off….if it can, switch off and unplug, put the brew boiler SSR back so you can use the machine for espresso and buy a replacement SSR for the service boiler side.
I also might feed back to the factory to see if it’s possible for the US machines to put in an inline fuse/breaker, resettable that trips main power if the draw is above 16A ish. As you know US plugs don’t have fuses like UK plugs and I assume your breaker was 20 amps?