Short answer
Start with the basics: power source (fuel, battery or socket), safety switches, and blade jams. For petrol trimmers, old fuel, a fouled spark plug or a dirty air filter are the most common causes. Isolate the power before inspecting the blades.
Battery hedge trimmers
- Is the battery charged and fully seated?
- Is the battery or tool too cold or too hot? Many protect themselves.
- Is the safety switch or two-handed control engaged correctly?
- Is the blade jammed with clippings? Remove the battery and clear it.
- Check for error lights; the manual explains the codes.
Corded hedge trimmers
- Is the socket live? Test it with another device.
- Has the RCD tripped?
- Is the extension lead damaged or too thin for the job?
- Check the cable and plug for damage; do not use a damaged cable.
Petrol hedge trimmers
- Fuel: is it fresh and correctly mixed? Old fuel is a common cause.
- Is the choke and primer procedure correct for your model?
- Check and clean the spark plug and air filter.
- Is the fuel filter blocked?
- If it flooded, follow the manual’s flooded-engine procedure.
When to get it serviced
If simple checks do not help, or if you smell burning, see smoke, or the blade will not move, stop and have the trimmer serviced by a dealer.
Always follow your own manufacturer’s manual: procedures, fuel mixes and service intervals differ between models, and a manual overrides any general guide.