A cast iron toilet flange can easily become damaged by a number of different things. If your toilet is unsteady and rocks, then this can cause the flange to crack. It's also very easy to damage the flange when you are doing anything with the flooring in your bathroom.
The flange is the part of your toilet which connects to the waste pipe. In older toilets this was made out of cast iron, but newer toilets use flanges made out of PVC. If the flange is broken or damaged, it can cause your toilet to leak.
Step 1 - Turning Off the Water
First turn off the water supply. This is pretty easy to do by turning the screw or locating the shut off valve. Get rid of the rest of the water in your toilet by flushing it. This will ensure that all the work is as tidy as possible.
Step 2 - Unscrewing the Toilet
Now start by unscrewing the bolts which are at the bottom of the toilet. There are normally 2 of these bolts, and they are sometimes covered. If there are covers, then they need to be pried off before you can access the bolts themselves.
If you're having trouble removing the bolts for any reason, then you can use a small hacksaw to cut through them. They will then need to be extracted before you can replace the toilet.
Step 3 - Removing the Toilet
The toilet can now be removed from the floor. You may have to rock this a little before it will move because the toilet is sealed to the flange. Once the toilet has been removed it's then possible to take it out of the way, but remember to put it on towels so that you don't make a mess.
Step 4 - Filling the Sewer
If the waste pipe is left open, this can cause gasses to enter your home which is not only unpleasant, but also very unhygienic. To prevent this happening, cover the hole with newspaper and tape it all the way around.
Step 5 - Removing the Closet Flange
The cast iron closet flange is connected with a series of bolts around the flange. If you cannot see where it connects, then you might first need to chisel into the concrete on your floor. Once the bolts have been removed, it should then be possible to pry the 2 parts apart using a chisel.
Step 6 - Replacing the Closet Flange
Now replace the closet flange with a replacement cast iron flange. You cannot use plastic because it's not possible to secure it to the cast iron. Bolt the cast iron flange onto your drainage hole. A new wax ring needs to be placed on top of the closet flange to seal your toilet.
Step 7 - Replacing the Toilet
The toilet can now be replaced and connected to the flange by using the wax ring. Make sure that it's positioned correctly so that all of the bolts and connections match up. Screw the bolts down and check that the toilet doesn't rock. Use household cleaners to wipe the floor and toilet to remove any dirty water or waste products that got out of the toilet while you were working, and you're done!