No one has used the bathroom for awhile, yet the toilet suddenly starts filling up like it was recently flushed.
To more superstitious folks, it might seem like the bathroom is being haunted. For us, it sounds like the problem is the water level in the tank.
When you flush the toilet a number of things happen at once. You pull a lever which lifts the flap. That flap covers the channel that takes water from the tank to the bowl. When it opens, all of the water gushes down to the bowl and into the drainage pipe, then the flap closes to seal the tank once more. A float in the tank controls a valve, which lets water back into the tank after you flush. When the enough water fills the tank and the float rises into place, it shuts the valve off. This is all usually over in less than a minute if everything works correctly.
If you're hearing your toilet tank continue to fill for a long time after you flush, a couple things could be wrong. First make sure that the shut off valve to your toilet is opened all the way so enough water can get to the tank to fill it up properly. Then, open the tank and see if the flap is positioned correctly. If it isn't, place it securely over the hole. Another possible problem is that your float might be stuck, keeping the valve open. If there is something obstructing your float or stopping it from rising, correct the situation. Your float and valve mechanism may also need to be to be adjusted so the valve shuts off at a slightly lower water level.
If the tank randomly starts filling by itself, it's a sign that the flap is failing. This means it's not properly covering the hole to the tank and is allowing water to escape and the level to drop. If the tank is filling up past where it should be, the pressure could cause even a brand new flap to fail. But if the water level is normal and the flap still isn't able to seal the tank, replacement is the best course of action.
If none of these quick fixes work or if you just don't feel comfortable trying to do the job yourself, don't hesitate to call John C. Flood, the professional plumber in Fairfax, VA who can address any issue with your toilet or other plumbing fixtures. Letting these problems continue can waste water and increase your bill, literally sending dollars down the drain.