Tauron has been disconnected from Poland's power grid since Aug. 6 due to a fault with the boiler and was asked by Poland's energy market regulator URE to explain the reasons for halting operations at its 910 MW Jaworzno power plant.

Tauron has not said publicly what the problem was but refuted claims by Rafako on Tuesday that bad quality coal had caused the problem.

Rafako CEO Radoslaw Domagalski-Labedzki said that several parameters of coal used by Tauron for the unit, including chlorine content, were beyond the set standards and that may have led to damages to the boiler.

"We have conducted a sample study of the coal which has shown that this coal (...) is in a such a plastic form... that it sticks to various parts of the boiler from the inside and causes sinter formations," Domagalski-Labedzki said during a news conference.

In response, Tauron tweeted: "Saying that the coal is the only ... problem (at Jaworzno power unit) is not true. Rafako is covering its own technological problems that they cannot deal with."

Tauron said that the repair of the boiler had been completed with the help of a substitute contractor.

(Reporting by Mateusz Rabiega, Patrycja Zaras, Marek Strzelecki and Maria Gieldon; Editing by Susan Fenton)