Many things could cause this issue. The most common culprit is the flapper not closing tightly around the flush valve. Try jiggling the toilet handle to see if it’s stuck. If this doesn’t help, you could need a flapper replacement. We’re also often asked how to prevent toilet clogs. Always be mindful about the items you’re flushing. Don’t overdo the amount of toilet paper being flushed or attempt to flush any foreign objects that could cause a clog.