My toilet won't flush completely. Sometimes it does. I have used a plunger extensively. Dob't understand why OCCASIONALLY it does flush, then it doesn't again. Can the toilet be the problem? Do toilets break ? Air flow? A clog that I just can't remove completely? Hate to call a plumber until I exhaust all options.

Take the top off the tank and flush. Does the flapper stay up until the water is emptied? Sometimes the chain interferes or is too loose. Tell us what happens.

Many things can cause what you areseeing so we have to eliminate them one by one. First step, confirm tank water level is 1/2" below the over flow tube. Next, do what ma is talking about to insure the flapper opens completely and stays up long enough to allow flush. Next, most toilets have a 1" hole in the sump area at the bottom of the toilet, this hole starts the siphon action, stick something like your finger in the hole to insure it is not clogged. Finally check all the small holes under the rim with a coat hanger to make sure all holes allow water out

That 1" hole is completely closed -- I need to open it. Any ideas

If it is blocked it may be from a cleaner tablet. Try breaking it up with a screwdriver or hanger. Be careful and don't break the toilet bottom!