[Humphrey Hacker]

Maybe a bit of a cheat but Last Of The Summer Wine?

[MorganLamia]

To flip the question around which long running shows have had the MOST title sequences?

Dragons' Den for example seems to enjoy the challenge of mixing them up a bit for each series although like a lot of shows these days have almost stopped bothering with them and just sort of merged them into the opening preview - long gone are the days when they would explain in great detail with fancy shots of how the individuals made their money!

If we're including non-UK productions, Power Rangers would be up there - 30 years non-stop with new opening titles each year, and each season has had several variations as new characters, gadgets, mecha etc are added. Although, production of the show has just finished, with the final season having been added to Netflix a couple of months ago, ending on 973 episodes.

However, way ahead of Power Rangers would be the original Japanese show that it uses footage from, Super Sentai, which has been airing almost every single week since April 1975 (normally 50-52 episodes a year, plus at least a couple of movies and special episodes outside of the regular episode count every year so... coming up to 2,400-ish episodes so far?) and is showing no signs of stopping any time soon.
As with Power Rangers, each year there's a completely new opening song and title sequence with all of them having many variants adding in new clips throughout the season. There are also many seasons that change the opening sequence every single episode by adding clips from the episode you're about to watch, which really ups the amount of unique opening sequences.

There are other tokusatsu productions that have been running a long time too, of course, such as Ultraman which began in 1966 and Kamen Rider which began in 1971, although they've had long breaks in production at times. Those too have similar style opening titles as I mentioned above - completely new each year with many variants, sometimes weekly.

[JAS84]

True. The current season, Ohsama Sentai King-Ohger, is Super Sentai season 47, and there's been 48 different OP themes - Go-Busters (Super Sentai season 36, and the source material for Power Rangers Beast Morphers) changed theirs mid-season. And that's just the change of songs, ignoring the multiple changes of visuals each year.

However, Super Sentai, Power Rangers, Kamen Rider, Ultraman, Metal Heroes, none of those technically count since they also change their name most years. The name Super Sentai is more like the new name Whoniverse for the Doctor Who franchise, with King-Ohger being the newest show in the Super Sentai franchise. It's an umbrella brand, but there's never actually been a show called Super Sentai (nor just Power Rangers).