State officials said the heat was back on for about half of a Tennessee prison that lost its main heating source on a frigid New Year's Day.
Tennessee Department of Correction spokeswoman Neysa Taylor said the rest of Riverbend Maximum Security Institution in Nashville has been expected to regain boiler-produced heat by Thursday night.
Taylor said it appears a valve malfunction was responsible for the loss of hot water pressure Monday, causing the prison's boiler to go offline.
Officials have tried to keep inmates and employees warm with extra blankets and portable heaters.
State data showed the maximum security facility held 787 inmates as of November 30. It also housed all 59 of the state's male death row offenders.