California Code, Public Utilities Code - PUC § 33015

All decisions and determinations of the board, upon notice and hearing, are final and conclusive upon all persons entitled to appeal to the board as to all errors, informalities, and irregularities which the board might have avoided or remedied during the progress of the proceedings or which it can, at that time, remedy.

Any objection, appeal, or protest not made at the time of any hearing is deemed to be waived voluntarily by any person who might have made the appeal, protest, or objection, and the person is deemed to have consented to the action taken following the hearing and any other matter on which objection, protest, or appeal could have been made.