If you install the toilet flange flush with the finished floor, or even below the finished floor, leak paths will form, because the flange won't be at the correct height to accept the horn at the bottom of the toilet.
If the flange is in decent enough condition then just use a fresh wax ring and shim it to get it level. I prefer soft rubber shims that are easy to cut. Make sure you check how level the floor is too. It could be that the flange is just angled slightly and you might not need to shim it at all.
A toilet flange that's too high can cause instability, as the toilet won't sit evenly on the floor. This can lead to an uneven seating experience, as well as increased wear on the wax ring.
If you notice shaking, your toilet may need minor or serious leveling. Start with small adjustments and, if the toilet still feels uneven, move on to more extensive adjustments later.
A best practice is to install the toilet flange on top of the finished floor. If you install the toilet flange flush with the finished floor, or even below the finished floor, leak paths will form, because the flange won't be at the correct height to accept the horn at the bottom of the toilet.
Use a flange extension kit: If the toilet flange has already been installed and is too low, you can get a flange extension kit. This will extend it to the proper height. Another option is to carefully stack multiple wax rings to achieve the right height. Then, set the flange into the lowest ring.
Caulking The Gap
If the toilet is stable, and the gap is less than 1/4 inches, you can simply caulk the gap with silicone caulk specifically designed for bathroom use. This will prevent water from entering the gap and potentially causing damage.
A toilet that is not level or centered could continue to leak water. Tighten the bolts with a wrench and replace plastic caps.
Toilet flanges are essential in securing the toilet to the floor; if compromised, rocking and leaks will soon result in ruining a newly renovated bathroom.
Use toilet shims to support the rear of the toilet higher in the air. Also shim the bowl alongside the bolts to avoid breaking the bow.
A faulty or broken flange may be attributed to a loose or worn-out wax seal. However, flaws in the foundation, like an uneven floor, may also cause the toilet's base to leak.
If you see pooling water around your toilet's base, clean up the water and thoroughly scrub the tiles until they are clean and dry. Wait a few minutes before reevaluating the space for leakage. If the pooling water returns after you clean the area, you probably have an under-tile toilet leak.
If the pipe has a 4-inch inside diameter:
Leave the old toilet flange in place and glue on the new one at the correct elevation for the floor, if it's plastic. The flange should be sitting with the bottom edge flush with the top of the floor.
The most common culprit for a loose toilet is the flange or flange bolts. Looking from the front of the toilet, check the flange bolts which are situated on each side of the toilet. If the bolts are loose, use a pair of pliers to carefully tighten the bolts until they are snug.
Because shims are used to fill gaps that don't exceed 1/4 inch and your gap is greater, we suggest you try the following fix. Put the toilet into place and make a pencil mark on the floor around the base. Shim it up using plastic shims, which are generally available in the plumbing section of your hardware store.
To help you visualize the difference between a toilet flange set too low and one set correctly, I've made a quick diagram, below. When we started working on our bathroom, we discovered the toilet flange was sitting below the surface of the tile, so toilet water was slowly leaking between the tile and the subfloor.
Flanges last for about 5-20 years. Worn-out flanges will no longer create a tight seal between the toilet and outflow pipe. As a result, when you flush, the toilet will leak at the base. By replacing the closet flange you will be able to stop the base from leaking.
The answer is, in most cases, that you should tile under the toilet flange and toilet tank. This allows for the toilet flange to be secured with the use of bolts. Only in a minority of use cases does the flange go beneath the tiles.
Toilet tank braces can be adjusted to fit the gap between your tank and wall. Clipped on back edge of tank, under lid, braces are practically invisible when installed. Anchor your tanks with Secure-A-Tank to protect against costly leaks and repairs.