Stop when the situation is unsafe or unclear
Do not continue homeowner troubleshooting if water is escaping outside the toilet, the bowl appears to be rising toward an overflow, a control is visibly damaged or stuck, or you cannot confidently identify the fixture or the condition. Avoid touching a stuck control or investigating inside the toilet. Contact a qualified plumber or the responsible property-maintenance contact and describe what you can see from a safe position. If there is no clear symptom pattern, that is also a reason to request an assessment before buying another part.
Start with the pattern you have already noticed
“Still running” can describe water that seems to continue flowing or a toilet that becomes quiet and then briefly refills again. Those are different observations, but neither one identifies a failed part. A refill after a flush also does not, by itself, show that the replacement flapper was wrong. Avoid treating the symptom as a diagnosis or buying another part on that basis.
Write down what you have already observed: whether the sound or flow seems continuous, whether it stops and returns, and whether the pattern changed after the replacement. Do not create a new test to classify it. If you are unsure what you observed, mark it as uncertain; that uncertainty is useful information for the person assessing the repair.
Match the records to the exact toilet and replacement
Before another purchase, gather what you already have: the toilet’s make and model from existing records, the replacement part’s maker and full model or part number from its packaging or invoice, and any product instructions supplied with it. If those identifiers are missing, say so rather than guessing from appearance or assuming that a part fits because it was sold as a flapper.
Have the installer, manufacturer, or plumber compare those exact identifiers with current instructions for that toilet and flush-valve design. Compatibility can be product-specific. A general guide cannot establish that a particular replacement is suitable, and a new part should not be chosen until the model and fit question has been resolved.
Separate the possible questions; do not turn them into a repair sequence
Korky’s How to Fix a Running Toilet gives examples to consider after replacement: a flapper or model-specific seal match, chain fit, and sealing-surface condition. It treats continued filling after the tank is full separately. These are manufacturer examples, not a diagnosis or universal instructions. Korky sells repair products. Checked 15 October 2026; no publication or update date is stated: Korky, “How to Fix a Running Toilet”.
Prepare a useful handoff
When contacting the person who installed the part, the manufacturer, or a qualified plumber, share:
- the toilet and flush-style identifiers you can find in existing records, or that they are unknown;
- the replacement maker and full part identifier from existing packaging or the invoice, or that it is unavailable;
- when the replacement was made and who performed it, if known;
- the already-observed pattern before and after the work, including whether the change is unclear;
- any visible damage or water outside the toilet that you have already noticed.
Ask whether the part was confirmed for the exact model, what the earlier repair included, and what evidence is needed to distinguish a sealing concern from a separate fill-control concern. Request an explanation of the next assessment before authorizing another part. This keeps the decision tied to the specific toilet and repair history instead of repeating an unverified swap.