(Adds further company comment)
HOUSTON, Dec 15 (Reuters) - Valero Energy Corp (VLO.N) said a gas oil hydrotreater was shut after a steam header failed on Monday morning at its 135,000 barrel per day (bpd) Los Angeles-area refinery in Wilmington, California.
Valero began restarting the hydrotreater on Monday afternoon, but does not expect to know how production will be affected at the refinery until Tuesday, said spokesman Bill Day.
"We don't expect the upset to have a serious impact on production at this point, but we won't know until tomorrow," Day said in a statement. (Reporting by Erwin Seba; Editing by Marguerita Choy)