water level rising in toilet tank even with water valve shut

Hi,

I have very little experience and was hoping I can get some direction on how to troubleshoot this problem. There was hissing noise coming from my toilet so I turned the toilet water valve off and used a pencil to mark the level of the water to make sure that the toilet wasn't constantly running. Strangely, the water level rose after awhile! So I flushed the toilet and marked the water level near the bottom of the tank. After about 30 minutes, it was obvious that the tank was refilling even with the water valve (under the toilet) completely off. Can someone please tell me what the problem might be? Thank you very much.

 

Sometimes the valve feels like it's completely closed & it's not. You probably need a new fill valve too.

 

I see. That makes sense. Thank you!

 

Also if you have a ball float style fill valve over many years it will slowly bend the rod up over time and cause an overfill condition. Bending it back down will correct this.