A little-known bureaucrat on the Department of Education payroll will make more money than Mayor de Blasio this fall after receiving a raise so “off the reservation” that it’s sparked a city investigation, The Post has learned.

Daniel Miller is the deputy director of the Board of Education Retirement System (BERS), the smallest of the city’s five pension plans with only 53,000 members, including aides, cafeteria workers, nurses, central DOE staffers, and crossing guards.

He is currently the highest-paid DOE employee after schools Chancellor Richard Carranza, who pulls down $352,763.

Last November, Miller, 38, received a 17 percent raise, boosting his salary from $217,125 to $255,000.

Miller now makes $26,000 more than his boss, BERS Executive Director Sanford Rich, and tens of thousands of dollars more than the heads of the four other city pension systems for cops, firefighters and other civil servants.

He takes home $67,000 more a year than his counterpart in the NYC Fire Department Pension Fund.

Even more jaw-dropping, Miller collects more than the heads of city agencies, including Police Commissioner James O’Neill and Fire Commissioner Daniel Nigro, who get $236,000 a year.

“That’s crazy,” said John Murphy, former executive director of the 360,000-member New York City Employees’ Retirement System (NYCERS), the largest pension system.

“This guy getting this kind of money has ramifications citywide. It’s going to create tremendous problems,” Murphy said, explaining it will generate a ripple effect of salary demands in other departments.

Rich gave Miller his latest pay hike in November, sources said. One insider said Rich gave the fat raise after Miller received a “lucrative offer” in Ohio.

Before granting the raise, Rich consulted with a few BERS trustees, the insider said. But Rich did not seek the approval of the entire 17-member board, which includes Carranza and eight mayoral appointees.

City Hall denied any involvement.

“Salaries for BERS employees are set at the sole discretion of the executive director,” said spokesman Jane Meyer.

“City Hall and the board were not aware of the salary increase.” A spokesman for Carranza declined to comment.

But unspecified board members filed a complaint with the city’s Special Commissioner of Investigation for city schools, which launched a probe, a spokeswoman confirmed.

Miller’s salary will rise again — to $262,650 –on Oct. 24, when a 3-percent pay hike for city managers ordered by de Blasio takes effect.

The mayor’s salary will remain fixed, under the city’s charter, at $258,750.

Miller is the son of Barbara Chiles, an organizer with District Council 37, the city’s largest public-employee union. About a third of BERS members are DC-37 workers, and a union representative traditionally holds a seat on the board of trustees.

Miller joined BERS fresh out of college and has spent his entire 15-year career at the pension fund, according to his LinkedIn resume. His salary there has doubled since Rich, a former Wall Street exec, was appointed chief in 2016.

Murphy said that Rich’s decision was “way off the reservation.”

“If he didn’t go to the trustees for this, he’s crazy,” Murphy said. “And if he didn’t clear this with the mayor’s office, he’s out of his mind.”

Rich and Miller did not respond to multiple requests for comment.