If the toilet begins to overflow immediately after a flush, it's likely that the toilet itself is clogged. First, stop the flow of water into the toilet to minimize flood damage. Remove the tank lid and press down on the flapper valve (don't worry, the water inside the tank is clean).
Often you can set the water level by adjusting the float. Toilets with ball floats and arms usually have adjustment screws or dials to raise or lower the arm. If your toilet mechanism has a cylinder float, squeeze the float clip to release the float so you can slide it up or down to the correct level.
The water level is the level of the P-trap on the waste side. You cannot change it [primarily because the P-trap height is a part of the ceramic toilet construction.] Nothing you do to the water inlet can affect the outlet height.
Usually, we think of a clogged toilet overflowing. However, the opposite can also happen where the blockage siphons water out of the bowl. Obstructed plumbing means that water cannot flow freely and circulate to the toilet. As a result, the water level in the tank will drop.
When you flush the toilet, the water level should reach its average level. However, if the water level remains high or rises to the bowl's rim, it indicates a clog in the drain. The clog can be caused by an excessive buildup of toilet paper, sanitary items, or other objects flushed down the toilet.
If water isn't going down in your toilet, you likely have a clog. Here's how to fix it: Use a Plunger: Place a flange plunger over the toilet drain and push down gently to create suction.
Substances like toilet paper and fecal matter will eventually dissolve within the toilet drain and clear the clog organically. However, blockages made from insoluble materials won't resolve on their own and typically require you to fix the clog manually or contact a professional before they worsen.
Check your water levels
Low water levels in your tank are common causes of toilets filling up with water when flushed. They can also cause slow-draining toilets. You can manually top up your tank with water to help the flush. Then, check the flush tube for cracks and bends that lead to leaks.
Boiling water can be a simple yet effective solution for loosening up a clog. Carefully pour some hot water into the toilet bowl from waist height and allow it to work its magic for a few minutes before attempting to flush the toilet water.
You need to get a bellows plunger that fits snugg into the drain of the Toilet and then you push up and down on it rapidly to remove the clog that by now is in the Trap inside the Toilet. After it's push around it will fall down into the sewer pipe and break apart, then the water level will return to normal.
Add a generous amount of liquid dish soap to the toilet bowl. Make sure to cover the entire area with the soap. Next, carefully pour a bucket of hot water into the bowl. The hot water will help soften the blockage and create pressure to push it through.
Adjust the Roller Clamp by pushing down and rolling the pin forward. Engaging the Rolling Clamp restricts the flow of water to the bowl. Repeat this action until the toilet bowl fills to your pencil mark at approximately the same time the tank water turns off.
You can adjust the water level by twisting the “Tank water level adjustment screw” connected to the float, indicated by the yellow arrows below. Turn the screw Clockwise for a higher water level and Counterclockwise for a lower water level.
A Clogged or Blocked Drain
Water will overflow from the toilet's bowl rather than the tank, causing a huge mess. In order to stop the overflow, you must treat the clog. For simple clogs, a plunger and some elbow grease will usually do the trick.
If the water is too high to use your plunger, then you're going to have to get some of the water out. Use a cup or a small bowl to carefully remove some of the water and pour it down the sink or bath drain. Once it's low enough, plunge away!
Pour ½ a cup of dish soap into your toilet bowl, if possible add a gallon of hot (but not boiling) water as well to help activate the clog-busting ingredients in the dish soap. Wait 20 minutes and then try out a test flush. You might need to scoop some of the water out with a cup or bowl to accommodate the hot water.
Problem with the Fill Valve: The fill valve is responsible for refilling the toilet tank with water after flushing. If the fill valve is not functioning correctly, it can cause the toilet to fill up with water after flushing. The fill valve may need to be adjusted or replaced to fix the problem.