White deposits need identification and a moisture assessment. Cleaning the visible mark alone may leave the cause unresolved.
Updated September 10, 2026
What you can observe safely
- Note whether stains return after rain.
- Photograph the pattern without scraping or applying chemicals.
What to avoid
- Do not climb onto the roof or enter the chimney.
- Do not alter gas components, venting, or safety controls.
- Do not use a test fire to diagnose the problem.
Possible causes to assess
- Moisture movement
- Soluble deposits
- Other surface staining requiring identification
A symptom cannot establish the cause remotely. An assessment of the complete system helps determine the appropriate repair.
Chimney repairA few common questions
Can this be diagnosed from a photo?
A photo can document a symptom and help prepare a visit. It cannot confirm concealed conditions or establish that a chimney or fuel-burning appliance is safe.


