Running Toilet - Diagnostic Tree

Symptom

Customer reports a toilet that runs continuously, intermittently cycles ("ghost flushing"), or won't stop refilling after a flush. A running toilet wastes 200+ gallons per day - by the time the customer calls, they've often noticed the water bill before the sound.

Likely Causes

In order of frequency for typical residential service:

• Worn flapper - most common, ~60 % of running-toilet calls
• Misadjusted float / fill valve - 15 %
• Cracked flush valve seat - 8 %
• Failed fill valve assembly - 7 %
• Chain too long / too short - 5 %
• Mineral buildup preventing flapper seal - 4 %
• Cracked tank or bowl (rare but catastrophic) - < 1 %

Diagnostic Steps

1. Listen + watch. Open the tank lid. Is water continuously trickling into the bowl? That's a flapper or flush valve issue. Is the fill valve cycling on/off? That's a float / fill valve issue.
2. Food-coloring test. Drop 5 - 10 drops of food coloring into the tank. Don't flush. Wait 15 minutes. If color appears in the bowl, the flapper is leaking - confirmed.
3. Inspect the flapper. Visible warping, soft / sticky rubber, or visible mineral crust on the seal surface = replace.
4. Inspect the flush valve seat. Run a finger around the rim where the flapper seals. Pitting, roughness, or visible cracks = the seat is bad; replace the whole flush valve assembly.
5. Check the water level. Should sit ~1" below the top of the overflow tube. Higher = misadjusted float, water spilling into the overflow continuously. Lower = inadequate flush.
6. Test the fill valve. Lift the float manually. The fill valve should stop. If it keeps running, the valve diaphragm is failed; replace the valve.
7. Check the chain. Too tight = flapper held open partially. Too loose = catches under the flapper, holding it open. Should have ~½" of slack at rest.

Resolution

Match the resolution to the finding:

• Water level too high: adjust the float per the fill valve instructions. Free.
• Chain wrong length: shorten or lengthen per manufacturer guidance. Free.
• Mineral buildup: hard-water area; descale or replace flapper. Suggest a softener consultation if widespread.
• Cracked tank or bowl: replace the toilet. Tank cracks aren't repairable.

Prevention

• On hard-water customers, recommend a flapper replacement every 3 - 5 years as preventive maintenance (it WILL fail; replacing on schedule prevents a sudden water-bill spike)
• Customer education: a phantom flush every 5 minutes = a slowly leaking flapper; call before the water bill arrives

References

• IAPMO Uniform Plumbing Code, Chapter 4 (Plumbing Fixtures and Fixture Fittings)
• EPA WaterSense High-Efficiency Toilet specifications