The refilling on its own is because it's leaking. Most common place is the flapper valve (that's what opens to mske the toilet flush). It stops sealing properly and leaks into the bowl and the drain so occasionally the tank needs to refill itself. They're super easy to change. The wax ring isn't likely the issue. You can also check the bolts that hold the tank to the toilet. They pass through from the inside of the tank and are sealed with a rubber gasket that can sometimes leak if the tank gets moved slightly. See if there's water dripping from the ends of the bolts. If so, give the tank a gentle rock. The tank shouldn't be able to move at all so you may need to snug them a bit. Often that's enough but the rubber gaskets may need replaced. Just remember if you get new ones not to over tighten. Just enough to firm up the tank and try to tighten them evenly so the force is directed vertically, not at an angle
Put a few drops of food coloring in the tank. If the bowl water develops color, the flapper seal is likely leaking. If colored water/stains appear on the outside of the toilet, hopefully they'll point towards the leak.
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Syndicofberyl t1_jdk6vyv wrote
The refilling on its own is because it's leaking. Most common place is the flapper valve (that's what opens to mske the toilet flush). It stops sealing properly and leaks into the bowl and the drain so occasionally the tank needs to refill itself. They're super easy to change. The wax ring isn't likely the issue. You can also check the bolts that hold the tank to the toilet. They pass through from the inside of the tank and are sealed with a rubber gasket that can sometimes leak if the tank gets moved slightly. See if there's water dripping from the ends of the bolts. If so, give the tank a gentle rock. The tank shouldn't be able to move at all so you may need to snug them a bit. Often that's enough but the rubber gaskets may need replaced. Just remember if you get new ones not to over tighten. Just enough to firm up the tank and try to tighten them evenly so the force is directed vertically, not at an angle