Has usually been the flapper needing replacement, in our house. Easy to do. One toilet, the flapper would often but not always, get stuck, that was solved by moving the chain from the end of the flush arm just a bit back. Another easy to do. Good luck!
When you say running, is the incoming water not shutting off? Or the flapper is not sealing the outgoing water? You may need to adjust the float level. If you lightly pull up on the float or if you have an arm pull the arm up and does the water shut off?
I would like to know how to get rid those pesty little sink/drain flies. I've tried baking soda and vinegar, drain cleaners and put plastic over the drains.
The seal in bottom of water tank is not closing completely. Could be worn or some small bit of debris is not allowing it to close tightly.
Remove the lid and wiggle the arm to close the seal. If it is not working, replace it.
https://www.familyhandyman.com/plumbing/toilet-repair/how-to-stop-a-running-toilet/view-all/
Has usually been the flapper needing replacement, in our house. Easy to do. One toilet, the flapper would often but not always, get stuck, that was solved by moving the chain from the end of the flush arm just a bit back. Another easy to do. Good luck!
When you say running, is the incoming water not shutting off? Or the flapper is not sealing the outgoing water? You may need to adjust the float level. If you lightly pull up on the float or if you have an arm pull the arm up and does the water shut off?
Heres a good tutorial on how to fix it, its not hard..... https://www.youtube.com/watch?v=DoqzGyC92GQ&t=48s