Eesti Energia's problem-prone Auvere power plant in Ida-Viru County restarted on Thursday after 45 days of construction and a weeks delay.
The oil shale plant opened in 2018 but has constantly experienced problems ever since.
After the latest round of work, bosses say the facility will become more reliable.
The plant was supposed to open last week, but additional work added a delay to the schedule.
"We were more or less able to manage the schedule, we went a few days over because the maintenance volumes got bigger," said Enefit Power manager Andres Vainola.
He said the construction work should not have affected electricity prices.
Usually, renovation work is not carried out during the autumn and winter, but Eesti Energia could not obtain the required parts any sooner.
Editor: Barbara Oja, Helen Wright