Hi, i have an Izzo Alex HX espresso machine that doesn't stop filling the boiler,
the pump stops, but it keeps right on filling it, it has a rotary pump and is connected to direct water connection. i don't think it's the HX tube because i had it out of the boiler about a month ago and it looks ok,
what else could it be?

what else could it be?

Your boiler fill solenoid valve is stuck open. Shut off water supply to machine (this is probably already done), remove solenoid, disassemble valve, soak in white vinegar for 30-45 minutes, rinse well, & reassemble.

Remove vacuum breaker valve and syphon water out of boiler till about half full. With the vacuum breaker valve still out, fire her up. Pump may run briefly to reestablish proper level but that should be it. You should NOT hear any water entering boiler. Replace vacuum valve, keep machine undressed for a while and you should be "good to go".