New tiles are not proof that every part of a roof has been renewed correctly. If a recently worked-on roof leaks, the original scope and the actual defect both need to be understood before deciding what happens next.
Start with the records of the job
Keep the quotation, invoice, guarantee and photographs. Record when the leak appears and the location indoors. Contact the original contractor with those details and ask what inspection and response they propose. A recent leak does not by itself prove dishonesty; the cause needs establishing.
Check what “new roof” included
Was the work a complete strip and replacement, a partial renewal or a covering-only job? Were the chimney, valley, roof windows and adjoining sections included? A retained detail can still need work even where a new covering has been laid nearby. If the scope was unclear, that is a reason to seek an explanation, not to guess at the cause.
Correct the cause, rather than disguise the symptom
A proper assessment should explain what has failed and the extent of the correction. On one job we documented, poor overlapping and old roofing left beneath later work meant stripping, renewing felt and battens, and doing the leadwork again. The lesson is specific: a new surface cannot make known defective preparation acceptable.
When to ask about wider replacement
If the defects are widespread, a series of small patches may not be the proposal you want to keep funding. Ask for the options and what each leaves in place. We will not promise that a limited patch resolves problems beyond its scope. Where we cannot agree a sound approach, we would rather decline the work than add another layer of uncertainty.