Police have discovered a “deviation” in the gas line at the Bronx marijuana grow house that exploded last week, killing Deputy Chief Michael J. Fahy.

In a briefing with reporters Monday about a number of crime issues, NYPD Chief of Detectives Robert Boyce didn’t describe the gas line anomaly but he said officials were excavating the gas main from the street in the building at 304 W. 234th St. in the Kingsbridge section. The pipes and other gas lines were being sent to a federal laboratory for analysis.

The house suddenly exploded on Sept. 27 after FDNY units responded to a report of a smell of gas. Fahy, 44, was killed after he was hit by a piece of the roof of the two-story dwelling that was blasted into the air. Inside the ruins, cops discovered numerous marijuana plants, liquid fertilizer and what Boyce said were “botanical” substances.

Officials had the 234th Street location under surveillance as a possible drug operation. Last week, two men, Garivaldi Castillo, 33, and Julio Salcedo, 34, were charged with felony marijuana possession based on their alleged activity at the building. Both are being held without bail. Officials said the second floor of the structure was essentially a greenhouse where windows had been sealed.

Prosecutors in the Bronx said in court that they were investigating possible homicide charges if a forensic examination showed that the gas lines had been tampered with in a criminally negligent way. Boyce said there was a gas leak and that the deviation in the gas line discovered couldn’t be explained.

“It could take some time,” Boyce said, referring to the probe into the gas line to determine if tampering contributed to the fatal explosion.

Boyce added that a similar investigation into the fatal 2015 gas explosion in the East Village in Manhattan took 10 months.