Hey guys,
I finally had the time to pull the left heater out, and visibly I see nothing wrong with it. Any tips how I could pressure test it? I don't just want to buy another one without confirming it's actually leaking.

Thoughts?
Thanks,
Zk

Easier to vacuum test than to pressure test...
Put your thumb over one end and the other in your mouth... Suck some air out of it like from a drinking straw and stick your tongue over the end... If it holds vacuum and doesn't let go of your tongue for 10+ seconds, then it's probably not leaking.

Secondly... If that boiler's not leaking, then the hose in the lower left is. Cut 3/4 inch off the end of the hose, reconnect everything and re-clamp the hose ends. See if it's fixed. (The outlet side of a steam boiler is pretty hot, it can eventually damage even the reinforced silicone hoses).

Thank you @JRising. The first thing I did was the vacuum suck, but I didn't think it was good enough.

Update:
...well what do you know. I just looked at the hose below the heater, the one that has the fuzz around it on the picture, and it's totally broken there. I thought the fuzz was just some insulation to protect it from vibration, or heat.

What's a good source for a new hose?

Thanks for the tips!
ZK

Jura's pretty difficult to get parts from, if you're not a dealer. You could ask your local dealer if it's possible.
Or just get something of similar size and properties meant to perform the same function for some other brand. Take the blown hose to a place that repairs other brands of super-autos.