NASHVILLE, Tenn. (AP) — Tennessee officials say the heat is 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 says the rest of Riverbend Maximum Security Institution in Nashville is expected to regain boiler-produced heat by Thursday night.

Taylor says it appears that 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 show the maximum security facility held 787 inmates as of Nov. 30. It houses all 59 of the state's male death row offenders.