youtube videos wont play while on cellular. Any fix?

If you know you are in a strong cellular data connection area, and this issue is concurrent on both the app as well as the website through Safari, I would start on some other troubleshooting steps. First, go to Settings>Safari>Clear History and Website Data and tap to clear this. Afterwards close Safari out from App Switcher. [double click the home button and swipe the Safari page up so it disappears] Finally, restart your iPhone by holding the Sleep/Wake and choosing Slide to Power Off [or use your Assistive Touch to do so]

After you have done this, see if YouTube still does not load through Safari. If it still is unable, you can go to Settings>General>Reset and Reset Network Settings and try again. If you are still experiencing this problem with YouTube through Safari even, then I have to come back to the cellular service question. Are you getting LTE, 4G, or 3G and how many dots of signal? YouTube is one of the most demanding sites I have encountered for cellular data. The fact that it is happening on the site as well as the app seems to indicate there is no issue with the App itself. Do you experience this only at certain times in the month? Could your carrier be throttling the use of YouTube in some way? Should you decide to troubleshoot your iPhone more than this, I suggest creating a backup first. How to back up your devices using iCloud or iTunes - Apple Support

mj512 wrote:

works well with wifi

Does the Youtube app state "No connection" when you are attempting to use it on Cellular, or is it so slow that you cannot use it? If it's just slow, that's the result of your current cellular data connection speed with your cellular service. The only means to resolve that would be to find yourself in an area that has a stronger cellular data speed connection.

If it was simply stating "No connection", check Settings>Cellular and scroll down to Youtube to make sure that its access to Cellular Data has not been disabled. Youtube will automatically detect your bandwidth and adjust for the best resolution video it can display on your device. Be careful of this when you are using data, as these videos eat a lot of data when they default to HD quality.