Phaser 7300 prints unfused pages

[OBProjects]

My Xerox Phaser 7300DX has started printing unfused pages, leaving loose toner on all the rollers. There is no message on the display, so the printer doesn't know that it's not fusing.
This occurs when there is a pause in printing between jobs or between pages of a job, for example when adding paper, changing a consumable, or even when processing a big image for the next page. A pause of a few seconds is enough to allow the fuser to stop. But if there is no pause in printing it fuses perfectly for hundreds of pages.
The problem occurs with two different fuser units, not new but not old either. I have cleaned the fuser/chassis electrical contacts with non-residue cleaner, and this does not help. Any ideas before I spend £300 on a Xerox service engineer?

 

[CULTOFLON]

You probably have bad fusing units. When the printer stops printing the fusers are rolled back to relieve pressure on the rollers. It sounds as if the fuser doesn't always roll forward on yours causing unfused prints. I have seen this problem multiple times.

 

[OBProjects]

Thanks CULTOFLON. It sounds like a mechanical problem rather than an electronic one. Maybe the gears that move the rollers forward are damaged.