If your toilet is constantly running, you should first check for leaks or see if the flapper or chain needs to be adjusted. These are the most common issues that would cause a toilet to run and are the easiest to fix. If these issues are not the problem, then it may be high water pressure that is causing your toilet to run. If not addressed, high water pressure can eventually cause leaks in other bathroom fixtures. The increased pressure can also cause the pipes inside your walls to vibrate against one another, which can damage your walls or even cause the pipes to burst.
If you get your water from a local water district or municipality, the problem may be on the provider’s end. Your water company may be willing to check the water pressure going into your home. If the pressure is high, they may also be able to install a pressure-reducing valve to bring your water pressure down to an acceptable level.
If you are on well water and in some municipalities, you may be responsible for resolving the pressure issue on your own. A licensed plumbing professional can verify if you have high water pressure and install a pressure-reducing valve if necessary.