Only one episode of Full House was actually shot in San Francisco, despite the show being set there. That's likely to be quite disappointing for many long-time viewers of Full House, as its San Francisco setting was a famous aspect of the classic sitcom. Family patriarch Danny Tanner (the late Bob Saget) even spent years co-hosting a morning talk show called Wake Up, San Francisco!, and images of iconic San Francisco locales like the Golden Gate Bridge appeared in Full House's opening credits.
It's also become well-known that the Tanner house—at least its exteriors—belong to a real home that can still be found in San Francisco, which has become something of a tourist attraction for Full House devotees, whether its current owners want that or not. Unfortunately, Full House's San Francisco setting was another case of TV magic, with the vast majority of the beloved series shot elsewhere in California. This is fairly common for sitcoms, especially old-school multi-camera shows, as few are actually shot in their storyline setting.
In reality, most of Full House's interior scenes were filmed on soundstages at the Warner Bros. studio lot in Los Angeles, California. Some second unit filming was done in San Francisco to use for exterior shots, and the opening credits sequence, but outside of that, every episode was filmed in Los Angeles. That is except for Full House season 8, episode 1, entitled "Comet's Excellent Adventure."
As the title makes clear, "Comet's Excellent Adventure" put the spotlight on Comet, the golden retriever that the Tanner family adopted in Full House season 3. The episode sees Uncle Jesse being kicked out of his band, The Rippers. While distracted by his personal problems, Jesse allows Michelle to take Comet for a walk, which was his responsibility. Comet ends up being far too much for Michelle (played by the Olsen Twins) to control, the dog runs off, and most of the episode is spent searching for him, with all the Tanners getting in on the act at some point. This leads to scenes shot on-location all over San Francisco, including the Golden Gate Bridge.
As for why "Comet's Excellent Adventure" was the only Full House episode actually filmed in San Francisco, it's because the script was specifically designed with outdoor location shooting in mind. It's unclear what exactly prompted this choice by the writers and producers, but considering season 8 was Full House's final season, it's quite likely they just wanted to feature the real San Francisco in an episode before the series came to an end. At the same time, shooting on location is much more expensive than shooting on a soundstage, so there was likely only enough in the season's budget to do this one trip into San Francisco proper. Either way, while "Comet's Excellent Adventure" isn't one of Full House's best episodes, it's still a fun change of pace and an interesting piece of the show's history.