They form part of the appliance's history and can affect assessment. The engineer needs to know about changes already made.
What the observation means
A knob, timer or door component can alter indication, fit or operation. Disclosure does not mean it is assumed faulty; it prevents an incomplete picture.
A useful next step
Keep references and fitting dates available. Do not conceal an owner attempt or continue swapping components to narrow the fault. Gas and electrical work require appropriate competence, and hazardous symptoms should stop further use while the current condition is assessed.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.