SRT Electric Train Co, which runs the Airport Rail Link, said a major maintenance programme for its eight trains was due to begin in April but has been pushed back to next October.
ACM Kamrob Leeyawanich, the company's acting president, blamed mistakes in managing the train maintenance plan and problems with spare parts procurement for the delay.
The company is still in the process of hiring experts from Siemens Co and Knorr-Bremse who will implement the maintenance programme, he said, while spare parts necessary for the maintenance project are yet to be imported.
Despite initial delays in budget approval, 380 million baht has since been signed off to fund the maintenance programme, ACM Kamrob said.
The trains are typically required to undergo major maintenance after running 1.2 million km, but he said the maximum mileage could be extended by 10%.
The train with the most mileage has travelled 1.28 million km.
Some minor maintenance work can begin in December, allowing the company to extend service periods, he said.
The full maintenance work should take a year, he said, about one or two months for each train.