Brian Collins was working for Nottingham-based Central (High Rise) on a contract to paint chimneys at Sutton Bridge Power Station in March 2008.
Collins, 52, had been setting up abseiling equipment with two other workers when he fell through an open grating plunging 34m to his death.
In a separate incident, nearly 18 months later, another employee fell 10m breaking his back after using the wrong abseiling equipment,
The man, who asked not to be named, was with another worker maintaining the rocks below Nottingham Castle but both had used the wrong abseiling equipment.
The first worker reached the ledge safely, but the second worker experienced an uncontrolled descent, falling up to 10m to the ground and breaking a bone in his back.
The Health and Safety Executive prosecuted Central (High Rise) for failing to protect its employees.
Leicester Crown Court heard the firm failed to ensure the work at both locations was carried out safely putting several employees at serious risk.
At the castle, the firm also failed to ensure the work was properly supervised. At the power station, it had also failed to make a proper assessment of the risks and to properly manage and monitor the work.
Central (High Rise) pleaded guilty to one charge in relation to the death of Collins and one charge in relation to the incident at Nottingham Castle. As well as the fine, the company was ordered to pay £32,000 costs.
HSE inspector Martin Giles said: “The work at the power station required careful planning and assessment of the risks involved.
“Tragically, the company failed to make sure the rigging of the ropes was done safely and the result was the needless death of an employee.
He added: “At Nottingham Castle, the two men should not have been allowed to abseil with the ropes they used, but Central failed in its duty to properly supervise the work to make sure it was carried out safely.
“Luckily the injured man has since made a full recovery but his injuries could easily have been much worse.
“Falls from height are the biggest cause of workplace deaths and it’s crucial that employers make sure work is properly planned, appropriately supervised and that sufficient measures are put in place to protect staff from the risks.”