Home, and done some measuring.

1. measurement:
   Just started the printer: 1,24 VAC
   Preheating the nozzle: 0,00 VAC
   After error beep: 1,24 VAC
2. measurement:
   Just started the printer: 1,57 VAC
   Preheating the nozzle: 0,00 VAC
   After error beep: 1,57 VAC

Old heater: 13,6 Ohm
New heater: 14,6 Ohm

So, no power to the nozzle heater. Now, how to verify the mosfet?