Does a waiver need to be a factual question?

Although an appellate court indulges every reasonable presumption against a waiver (Glasser, supra, at p. 70, 62 S.Ct. at p. 464-65), it is ordinarily a factual question whether there was a waiver, limiting appellate review to a search for substantial evidence to support the trial court's determination, unless, as here, there is no conflict in the evidence, and a question of law is presented. (See People v. Duren (1973) 9 Cal.3d 218, 237-238, 107 Cal.Rptr. 157, 507 P.2d 1365.)