Fill valves often get clogged with debris and sediments. Thankfully, cleaning them is easy. Once the cap of the fill valve is removed, carefully inspect for debris that might be stuck in and around the body of the fill valve. Use an inverted mug over the opened fill valve and turn on the water supply. This will force the water to circulate through the body of the fill valve and release the debris or sediments. Repeat this process at least twice to clean the fill valve.