What's wrong with my toilet?

The usual cause is that the tank isn't filling high enough, so there isn't enough water weight to create a proper siphon. Take the lid off and check that the water stops about an inch below the top of the overflow tube. The other common cause is mineral scale blocking the small holes under the rim, which starves the bowl of water even though the tank empties normally.

It can be. Gurgling means air is being pulled through the water in the trap, which happens when a vent is blocked or a drain line is partly obstructed. If only the toilet gurgles slightly it is worth investigating but not urgent. If flushing the toilet makes a nearby tub or sink react, the shared line downstream is blocking and that frequently precedes a full backup.

It is a bad idea. Chemical drain cleaner rarely clears a toilet clog because it cannot reach past the trap in useful concentration, and it sits there as a hazard for whoever opens the fixture next. A flange plunger clears most toilet clogs, and a toilet auger clears most of the rest.

Check what happens to other fixtures. A toilet-only problem leaves every other drain in the house working normally. If flushing makes a tub gurgle, a sink drain slowly, or water appear anywhere else, the blockage is downstream of both fixtures and it is a main line problem rather than a toilet problem.

If you do it yourself, usually between $8 and $20 for the part — a flapper, a fill valve, or nothing at all if the water level just needs adjusting. If you call someone it is normally a minimum service call since the labour is short. A toilet that runs continuously wastes water every day, so it is worth doing promptly either way.