I just had the floors in my bathroom replaced and now the flange is too high. When I put the toilet on top, the front touches the floor, but the back does not. The flange and piping are PVC, and the floor is concrete with vinyl on top. I'm not sure how to approach this problem. There are many solutions for a flange that is too short but not for one that is too tall.
I found this 2 part video on YouTube that helped me understand what to do.
I ended up cutting off the top of the flange with a PVC pipe cable saw. I then used a mini hacksaw to cut some segments into the fitting and wedged the pieces out. After removing 2 small parts of the ring, the rest just wedged right out without much effort. I cut down the pipe to be flush with the floor using a pull saw. I put a level down and found the concrete was not level around the pipe. I used a rub brick and the mini hacksaw, which I could angle to cut the inside of the pipe, to get the pipe and surrounding concrete truly level with the rest of the floor. This took a while.
When I finally got it level, I put in a Twist N Set Closet Flange. I drilled 4 pilot holes and put in concrete screws. The toilet is now level and not going anywhere. Now I just have to fix my guest bathroom which has the exact same problem. At least I got a good deal on the house.
Unfortunately, with a flange that is too high, you typically have two choices-
There is a third option that sometimes works, and that is to use a waxless sealing ring, though they tend to be leaky, and it sounds like your flange is too tall even without the ring.
Depending on how the flange is coming up through the floor, and the access you have from underneath (Though with concrete I am guessing you have none) you may be able to remove the flange, cut the pipe shorter, and put a new flange in.
There is no need for difficulties like raising the whole foor just to raise a toilet, or cutting the pipe to install a new flange which is lower.
I recently raised a toilet almost 1 cm off the floor easily using grout. I had to do this after attaching a repair ring onto the flange, which has broken closet-bolt slots, but is otherwise solid. The repair ring and the bolts holding it in place effectively raised the height of the flange, not allowing the back of the toilet to touch ground.
I should mention that this is on a concrete floor which has lino over it, not tile. I used portland-cement-based sanded grout.
This is the resulting appearance: a very thick, prominent, grout line:
For comparison of grout bead size, here is an identical toilet in another location, also grouted with the same material, but which is not raised. This toilet already sat on the floor, before the grout was applied, which was done for cosmetic reasons and any additional stability it might provide.
Tip: when leaving gaps in the grout around shims, neatly curve the end of the grout bead inward under the toilet: don't leave it ragged. This curve make it easier to create a smooth, invisible overlap when you close the gap the next day, so it looks like everything was grouted in one pass. (This is analogous to feathering the edge of a painted area, so then it blends nicely when the adjacent unpainted area is later covered.)
Tip: in the first 24 hours while the grout was hardening, I sprayed it several times with a spray bottle to moisten it (another dollar store item). Cement requires water to achieve hardness; it stops becoming stronger once the water is gone. Big concrete pours can retain water for weeks and months, so they can achieve their full 90 day cure, but small grout jobs can dry out. Maybe the spray bottle irrigation did nothing, but it took little additional effort.
Tip: the package of grout will give you ridiculous mixing instructions, like to add the whole 7 lb contents into a pint of water. You need only a small quantity that you can mix in a yogurt container. By volume, it looks like about 6:1 to 7:1 powder to water for Polyblend Sanded. I don't recommend pre-mixed; it contains VOC's, and is poor value for the money. The consistency should be such that your stir stick easily stands up in it, and it doesn't move when you tilt your mixing jar 90 degrees. I used less than two cups of powder in total, and much of it went to waste due to left overs and trimmings. Start by erring on the side of too little water. If the grout is hard to mix and lumpy, add water, in tea-spoon-sized increments.
Optional: leave a gap in the grout in an inconspicuous place (back of the toilet) for releasing any leakage. I'm aware of the arguments for it, but I decided against it. I'd rather not have a water spill on the floor going the other way under the toilet, or create a crevice for pests to crawl into.
From now on I will use grout for toilets, unless it is contraindicated for some good reason. It not only can be used to raise toilets, but it will take care of any unevenness in the floor (or the toilet itself) even if the flange isn't too high. If the toilet rocks due to an uneven floor, it can break the wax seal and damage the flange. Evidently plumbers in the "olden days" used to commonly do this as the "right way, darn it" to install a toilet. In fact, some took the time to follow a procedure which goes something like this: