The fuser had already gone very bad and was smearing and crumbling up paper, but the printer did not show any message that there was a problem with the fuser or that it should be exchanged.
On the CentreWare page of this printer I noticed that under Status > Supplies under the Maintenance Items the Imaging Unit Kit and Waste Toner Box are listed, but Fuser and Transfer Belt Unit are missing. On our other WC6605 these two items are shown there.
I'm not sure if the two problems are related, if I can do anything about them myself or if I should ask for a technician.
The fuser may fail even if not reach it's life, because of lot of factors like quality of paper, time of printer stay powered, number of pages per print job, number of power on/power off, print coverage.
Fuser and transfer unit are listed just under the Diagnostic Mode accessible for service engineers.
On the other hand, the life of user will be reset when a new fuser is installed
thanks a lot for the quick answer.
I'm still wondering why on the CentreWare page of our other WC6605 I can see Fuser and Transfer Belt Unit under Supplies Status > Maintenance Items and both of them are shown at 100% Level - so I assume these numbers do not mean anything?