A bad fill valve can cause a number of symptoms in your toilet. These symptoms can include:
1. A slow flush: This is usually the first symptom you'll notice and it's caused by water leaking past the fill valve into the bowl. As the water level in the bowl drops, the flush becomes weaker and takes longer to clear the bowl.
2. Water accumulation around the base of the toilet: If you see water pooling around the base of your toilet, it's likely that your fill valve is faulty and needs to be replaced.
3. An overflowing toilet: A broken or damaged fill valve can cause your toilet to overflow when flushing. This is not only messy, but it can also damage your floor and furniture if left unchecked.
4. Frequent cycling of the tank refill: If you notice that your tank seems to be refilling more often than usual, it could be a sign that your fill valve isn't shutting off properly, causing water to leak into the bowl and necessitating a refill more frequently than normal