Lyondell Basell Industries expects to boost production at the 263,776 barrel per day (bpd) Houston refinery this week following the restart of a vacuum distillation unit attached to the large crude unit on Sunday night, three Gulf Coast market sources said on Monday.

The refinery has been running at 32 percent, or 85,000 bpd, since April 15 when the 91,000 bpd VDU was shut, the last of a string of four major production unit outages last month that began with an April 8 fire on a coking unit.

A Lyondell spokeswoman declined to discuss operations at the refinery on Monday.

The refinery expects to boost production to at least the 147,000 bpd capacity of the Unit 537 CDU that processes heavy crude oil at the refinery, the sources said. Production on the unit has been cut back because the VDU could not process residual crude being produced by the CDU.

Unit 537, like the 120,000 bpd Unit 536 CDU, does the initial refining of crude oil crude coming into the refinery and provides feedstock for all other production units.

Unit 537 can operate beyond its faceplate 147,000 bpd crude oil intake capacity. Before its VDU went down, Lyondell had been planning to operate the unit at higher levels to make up for lost production.

Energy industry intelligence service Genscape said Unit 537’s VDU restarted on Sunday night after repairs. The refinery began restarting the VDU on Saturday.

Unit 536 was shut on April 11 after leaks were found in its 91,000 bpd VDU.

Both VDUs were found to have leaks in piping and malfunctioning pumps, the sources said.

The 42,000 bpd coking unit is expected to be shut for three months of repairs following the April 8 fire, sources have told Reuters. Originally, it was thought the unit would return in six weeks.

Unit 537 and its VDU along with the coker were all shut for a six-week overhaul that ended on March 1.

A 57,000 bpd coker remains in operation at the refinery.

Cokers refine residual crude coming from the VDU or convert it into petroleum coke, a coal substitute.