The pension hearing for former police chief Thomas LaCroix that had been slated for last week was rescheduled to the Waltham Retirement Board’s Sept. 25 meeting, and will be closed to the public, said the board’s administrator, Joseph Juppé. Nicholas Poser, the lawyer representing LaCroix before the board, told the board that he had a scheduling conflict and requested the new hearing date, Juppé said. LaCroix, who in June was found guilty of two counts of assault against his wife, resigned as the city’s police chief on July 10, the same day that Concord District Court Judge J. Elizabeth Cremens sentenced him to 18 months probation. The Waltham Retirement Board then voted unanimously to hold a hearing to determine whether the conviction would disqualify LaCroix from receiving his city pension. Michael Sacco, the board’s lawyer, previously said officials are gathering information about LaCroix’s case from the court, and are reviewing manuals for police codes of conduct to help make their determination. He said LaCroix is allowed to ask for his pension hearing to be closed to the public, but he noted that the written decision will be made public. LaCroix, 50, worked for the Police Department for 26 years, and was appointed chief in 2007.