The worker died while replacing rubber sleeves on the machine's rollers. To help put the rollers in the correct place, he turned on the power to the harvester using the controls of the tractor to which it was attached.
One of the farm business partners was helping in the task but later left the worker to complete the job alone. When he returned an hour-and-a-half later, he found that the man had become trapped between the rollers.
A Health & Safety Executive (HSE) investigation found that the partner had not conducted a proper assessment of the risks involved in carrying out maintenance and testing work on the potato harvester.
Investigators also found that there was no safe system of work in place for maintenance to be carried out.
HSE inspector Peter Dodd said: "This case should act as a timely reminder to farmers of the very real dangers posed by their machinery when they are preparing it for harvesting, undertaking repairs or maintenance or attempting to clear blockages."