Printer not duplexing when change fuser settings

[TaxOfficePrinte]

This is related to troubleshooting and even a discussion with an HP rep concerning a printer that wouldn't duplex.  The story goes as follows:

Did a windows 10 update, a firmware update and a driver update to a new computer and related (older) HP P3015DN printer.  I changed quite a few settings to secure the printer from potential network intruder.  This includes changing the admin password (which I still have yet to get to work as it locks me out even though I'm sure to enter the correct password... so not sure the parameters the password requires).  In changing many of the settings, the duplex stopped working.  I checked and tried other drivers and all the other things routine in many other posts in this community.  After talking with a rep we decided to just do a factory reset and I would change the settings one by one to figure out what broke it.

It turns out changing the fuser settings to low on the light paper I was using (to reduce curling) broke the duplexing of the machine.  This was after half a day of working through what the possible setting that messed it up could be.  It still does duplex properly with normal or low1 (which I assumed low1 was the lowest and low and normal was above that).  

Does anyone know where to obtain more helpful information concerning these fuser settings and why it would cause such an issue?  I assume it has something to do with how much the paper curls or the setting of the ink, but it seems rather strange to me that this setting would break duplexing.

I appreciate the help.

[Repairatrooper · Accepted solution]

Probably the designers felt that there would not be enough retained heat at that fuser temperature to provide reliable bonding. Disabling duplex would prevent toner contamination. 

In terms of password, a common thing we run into is accidently having caps lock on when setting password effectively making all upper case letters lower case and vice versa.