Troubleshooting the Open Heat Error in the Dell MFP Â 1600n Printer
The open heat error is typically caused by a  open circuit  in the AC power supplied to the fusing assembly,Dell MFP  1600n  Fuser  Assembly Unit, N5796-MK . Usually the thermostat has opened and failed to close or the lamp has failed. The best thing to do is remove the fusing assembly and with a volt meter check the continuity across the lamp and the thermostat.
The thermostat sits right on top of the fusing assembly, see below. The thermostat is a thermal fuse. If the fuser  overheats which they tend to do in this machine the thermostat will open. When the printer cools off the thermostat is supposed to  close. Often times that fails to happen. If that is the case with your thermostat take a can of compressed air, hold the can upside down and give the front of the thermostat a shot of extremely cold air. A lot of times that will reset a stuck thermostat. Check the continuity again and if it passes then plug it back in and start the unit back up. If it still fails or the fuser has extreme signs of wear then it’s probably time to replace the fusing unit.
Open heat error When warming up, it has been lower than 68 °C over 25 sec
Rear Cover
1. Remove the four screws securing the Rear Cover.
2. Remove the Rear Cover from the Frame Assembly.
3. Unlatch the (Cover Face Up) securing the Rear cover.Then lift the (Cover Face Up) out.
Dell MFP  1600n  Fuser  Assembly Unit, N5796-MK 
1. Unplug the two connectors from the Main PBA  and SMPS, as shown below. Then remove the 4 screws securing the Fuser  Ass’y and remove it.
2. Remove the 2 screws securing the Thermostat. Then lift the Thermostat out
3. Remove the 2 screws securing the Halogen Lamp. Then take out the Halogen Lamp from the Heat Roller
4. Remove the 4 screws to remove the fuser cover as below. Remove the 2 screws to remove the guide input.
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Dell MFP  1600n  Fuser  Assembly Unit, N5796-MK
