If your tank runs every once in a while, but seem to be getting more often or runs constantly- 1. check flapper & chain 2. If ok you probably need to replace the flow valve Hope this solves it
Tools. Look at flapper- that may be the only replacement. If not, then proceed on to the flow valve. I had to replace tank seal also due to water leaking outside tank.
1st turn water off at the wall. You will need towels for excess water from line and tank. 2nd disconnect water from tank. 3rd drain tank(flush and towel the excess).
Remove flow valve (attached under tank).
If your flapper covers and is in good shape you may not need to replace. I just did- mine left a gap and tank ran to keep replacing lost water.
After all that, I found mine had a slow leak from this seal. Bought a new seal to fit and replaced it too.
After removing from seat. When you unscrew this the PVC tower comes undone too. Be sure and disconnect chain and flapper to make it easier.
Check that you have the correct brand and seal style.
Getting the old seal out was no picnic. It would not release from old screws. Now place new seal and screws. Secure joining new center plastic nut and the PVC tower inside. Place tank back on seat.
Make sure all attachments are secure and tight.
Replace flow valve, attach flapper, chain and secure bolts.
Reconnect water and slowly turn on to refill tank. Leave a dry towel under back to be sure you have no leaks or drips.