We have problems with C-3851 on a Bizhub C250. You can reset the code and the machine will work for a couple of weeks, but then the problem is back. Have replaced the Fusing Unit and upgraded the firmware to Phase 2.01.
Any suggestions?

Have you tried installing a line monitor on the outlet. Voltage discrepancies can cause this.

I had this same problem. I reset it twice and even replaced the fuser unit. Error code keep coming back. There is a support solution from Konica about this.
Change software setting. Service Mode System 2 Software Switch Setting
switch no: 50
bit assignment: 00000001
hex assignment: 01
note: hex value will change automatically, if you change the bit

I got the same problem, there was a small power surge and now i got the same c-3851 error , how do you reset the code?

Hold down [Utility/Counter] while turning the main switch on. Press [Reset] on the touch screen, and turn main sw. off/on.

i need firmware for bizhub c250
can send it to email
plz

gateway.vly@gmail.com
thanx