Use a moss killer which also feeds the lawn, then a week later a weedkiller...its ok to use a moss, weed and feed but they are not as effective.. DO NOT connect the grass box, it fills up in seconds and jams the machine so that it overheats, if it does overheat it will stop, let it cool overnight and it will probably be ok... I have had this scarifier for about 2 years, during this time I have found and resolved several issues...I think these are the important points good and bad. when finished change the tyne unit for the one with blades. go up and down then side to side, this cuts slots to get water to grass roots.... sprinkle grass seed where required and maybe some lawn dressing soil.... ok ready to start..go forward ONLY, slowly...don't run over hard surfaces like a path or tyne will break.