Several conditions can produce the same observation. An on-site assessment should test plausible causes and document limitations before a repair is selected.
Can I keep using the fireplace or appliance?
Do not test a possibly blocked flue with a fire. Respond immediately to smoke or carbon-monoxide alarms and seek emergency help when needed.
What should I photograph or record?
What changed and when Visible debris without reaching into the system Animal activity, storms or construction history Last known inspection and use
What type of company should I contact?
Look for a company with relevant experience in chimney inspections and your appliance type. Confirm services, qualifications and current insurance directly.