The three patterns and what each means
Pattern 1: Double-flush (you press once, toilet flushes twice in a row). The flapper isn\'t closing after the first flush — usually flapper chain too short, holding the flapper open until water drops past it.
Pattern 2: Ghost flush (toilet refills on its own every 5-30 minutes when no one used it). Slow leak from tank to bowl — almost always a worn flapper or mineral-scaled flush valve seat.
Pattern 3: Never finishes filling (constant trickle from fill valve, water level keeps rising slowly). Fill valve isn\'t closing — debris in the valve seal or the float isn\'t actuating properly.
Fix Pattern 1: Double-flush
Open the tank, watch a flush in slow motion. The flapper should pop up when you press the lever, then fall back when about 80% of tank water has drained. If it drops mid-flush and the lever returns to neutral but water keeps siphoning to a second flush — check the chain. Slack should be 1/2 inch. Too tight: chain holds flapper open after lever returns. Add 1-2 chain links of slack. Test 5 flushes to confirm.
Fix Pattern 2: Ghost flush
Food coloring test: drop 5 drops of food coloring into the tank, wait 20 minutes without flushing. If color appears in the bowl, you have a flush-valve leak. Replace the flapper first ($5, 10-minute job). If new flapper still leaks, the flush valve seat itself is the problem — mineral scale or pitting on the seat surface. Either scrub clean with a Scotch-Brite pad, or replace the entire flush valve assembly (45-minute job, $25).
Fix Pattern 3: Never finishes filling
If you hear constant water flow from the fill valve area and water is rising above the WL line, the fill valve is either failing to close (debris in valve seat) or set too high (water level above the overflow tube). First, lower the float — set water level to 1 inch below overflow tube top. If valve still won\'t close, shut off water, remove the fill valve cap, flush debris from the valve seat, reassemble. If still failing, replace the fill valve ($12, 25 minutes).
Edge case: high-water-pressure-induced cycling
In homes with municipal water pressure above 80 psi, the fill valve can\'t fully close against the line pressure — you get a constant 1-2 minute cycle as the valve almost closes, opens slightly, almost closes. Fix: install a pressure-reducing valve at the main water entry ($150 + install). Long-term, high pressure also damages dishwashers, washing machines, and faucets — worth fixing for whole-house benefit.
Edge case: phantom flush in a low-use bathroom
If the toilet ghost-flushes only in a low-use guest bathroom or vacation home where it sits unused for weeks: water evaporates from the bowl trap, then refills automatically when the air gap breaks. This is normal physics, not a defect. Fix by adding 1 oz of mineral oil to the bowl monthly to slow evaporation.