Low water level in toilet bowl

the water level in the pan is set by the exit pipe level and if it is raised it will only flow out again to that pipe level
if you are ferefing to the cistern water level
remove the top and adjust the float level or level control unit

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The toilet you just installed is a 1.6 gallon flush water saver and will not have the same amount of water in it that your old 3.5 gallon toilet had. The water level may not be able to be raised as this is the nature of the beast.

If you can raise the level it will only be a little and will be done in the tank area by increasing the water level in the tank. If the water level in the tank is at the mark provided it a done deal.
The amount of water refilled into the bowl is done by the tube that runs from the fill valve into the overflow tube of the flush valve so if you put more water into the tank more water will be put into the bowl but the bowl will only hold as much water as the trap weir will let it hold (what the factory has sit it at and is not changeable

All toilet bowls have a preset water level determined buy the design of the internal s-trap and can not be change. However if the water level in the tank is not as high as it should be this will affect the water put into the bowel as the bowel in refilled by the flush valve and if it is set to stop before it get filled to the proper setting the bowl water level may be low.
A quick test is to see if the water level in the tank is up to the line in the tank most all toilet tanks have a line either stenciled or marked with a indentation in the porcelain. Another way is to mark the level in the bowel with tape or a marker then pour water slowly into the bowel not fast enough to flush it wait to see if it stays higher then the mark you made or settles back to that level.

Hi, W/D here.
Check the water level in the tank. The force to flush waste comes from there. Normally the fill line is cast into the back of the tank, but sometimes it is on the overflow tube. Raise the level if it is low.
Also, make sure that the tubing from the fill valve is connected to the over flow tube (the tall tube).
Best regards, --W/D--

Check to be sure small tube is flowing inside the ovefow tube. This is the water that flushes the rim holes, and refills the bowl. If you don't have flow clean or replace the float valve.

Too little water in the toilet bowl to start with may be due to a lost or mis-connected fill tube that directs some water into the toilet tank standpipe (and thus into the bowl below), while the toilet tank is being re-filled. Check for that little tube.

Check the web site out below for more information on this topic.

http://www.inspectapedia.com/plumbing/Toilet_Slow_Flush.htm

First off,If the air vent was clogged the toilet would back up and overflow and when it did flush, it would make a gurgling sound.
secondly the water level in the bowl is not important as long as it covers the opening,The water is only there to keep out sewer gases so they don't enter your home and the shape of the trap will always maintain the proper amount of water needed to prevent this.
The previous water level may have been due to a partial clog that has since been removed.

First, fyi, adjusting the knob? in the tank, or the fill level will not increase the amount of water in the bowl. The bowl fills to a certain point, and then as more water is added it starts to go over the built in trap, and down the drain. When you flush the toilet, all the water in the tank dumps into the bowl, and the existing water is pushed over the trap and down the drain. All of this being said it sounds like you may either have an internal crack, between the bowl and trap; you may have a crack that is draining under your toilet, (water spots?), or you have a more serious plumbing issue, improper venting, which is causing a vacuum, and pulling the water out. Hope this helps.

The water level in the bowl is limited by the height of the internal trap down stream from the bowl. There is no adjustment possible. If the problem is odors, you can either flush more often, turn on the exhaust fan, or buy a different brand or model of toilet.