Red light comes on but coffee doesn't brew

If there is a thin water line in your coffee maker, then it can get clogged or could have mineral build up. Keurig coffee maker, you are going to want to descale it every 6 months. Calcium can build up.You need to run a large cup of white vinegar through coffee maker lines. When you run vinegar through there, the coffee will taste nasty, so I would run water in there several times, after the vinegar finishes. Run through until does not taste nasty anymore. Yeah, I do this with my coffee pot 3 times a year. You judge how often you should.
Good luck.