The wood chipper seems clogged. Why is that?

The material you have put in is probably of low weight. Like for example big soft leaves, they could not reach enough velocity to be discharged through the output chute. That results in material staying behind in the shredder box, which cuts it even to pulp which eventually cannot come out anymore. If this occurs, the machine should be stopped as soon as possible and the shredder box should be cleaned.
The wood chipper is built for chipping fresh branches. Wood chips have enough mass to create a nice continuous output flow. Chipping leaves is possible as long the combination with the amount of chips are in balance.
For shredding and chipping leaves and similar kind of material we suggest to use our compo chipper GTS1300C or composter GTS300 or leaf shredderGTS800.
Read more information in the user manual.