The 1 most common part(s) or condition(s) which cause the symptom String trimmer head won't stop spinning are listed below starting with the most likely. Check or test each item and watch any available videos.
To see parts for your string trimmer, you need to enter your model number on the right. The system will then display parts that are associated with your string trimmer.
If the string trimmer head won't stop spinning the clutch assembly might be worn out. The clutch assembly is located near the engine at the end of the trimmer shaft. It is sometimes possible to clean and repair the clutch assembly, but given the relatively low cost and the difficulty of the repair, it may be easier to simply replace the entire clutch assembly.