Toilets are simple machines, which is why the problems tend to repeat. Water goes in, sits in a tank, drops through a valve when you flush and refills. When something goes wrong, it nearly always traces back to one of a handful of parts, and knowing which one saves a lot of guessing.
The one that won't stop running
A toilet that hisses or refills on its own every so often is almost always leaking from the tank into the bowl. The usual cause is a flapper that has hardened or warped and no longer seals. A few drops of food colouring in the tank will confirm it: if colour shows up in the bowl without flushing, the flapper is letting water through. Replacing it is cheap and quick.
If the flapper is fine, look at the fill valve and the float. A float set too high lets water spill into the overflow tube, and the valve keeps running to replace it. Adjusting the float or replacing a worn fill valve usually solves that. Old brass fill valves in older houses can also corrode internally, and a modern replacement tends to be quieter and more reliable.
Rocking, seeping and stains on the ceiling below
A toilet that moves when you sit on it has a problem at the floor. Either the bolts have loosened, the wax ring has compressed or the flange underneath is cracked or set too low. Tightening the bolts can help briefly, but if the seal has already broken, water seeps out with every flush. In a house with a bathroom over a finished room, the first sign is often a brown stain on the ceiling below.
Older houses are especially prone to this. Floors settle, tile gets added over old flooring and the flange ends up below the finished surface. The fix may mean a flange extender or a new flange altogether, and sometimes a look at the subfloor if it has been wet for a while. That kind of underlying work is part of a broader conversation about plumbing in Montlake and similar neighbourhoods, where interwar houses have had their bathrooms redone several times over the decades.
Clogs that keep coming back
An occasional clog from too much paper is normal. Clogs that return every few weeks are a different story. They can mean a partial blockage further down the drain, a vent that is not letting air in properly or, in older homes with clay or cast iron sewer lines, roots working their way into the joints. If other drains in the house gurgle when the toilet is flushed, the problem is probably in the main line rather than the toilet itself.
A plunger with a flange is the right first tool. If that does not hold, a closet auger can reach a little further without scratching the bowl. Beyond that, a camera inspection of the line is the sensible next step before anyone starts guessing. This guide on handling urgent toilet problems explains what to do when water is rising and you need to stop it fast.
Repair or replace
Most toilet problems are fixable with inexpensive parts. Replacement starts to make sense when the porcelain is cracked, when the bowl is an old high-volume design that never flushes cleanly or when the same unit keeps needing attention. Newer models use less water per flush and often clear waste better than older ones, thanks to improved bowl and trapway designs.
If you are replacing, check the rough-in measurement from the wall to the flange bolts so the new toilet fits, and decide on bowl height and shape before you shop. It is also a good moment to replace the supply line and shutoff valve, which in older houses may not have been turned in years. For a wider view of the options, this piece on professional fixes for common toilet issues covers when a repair is enough and when it is not.