Strange residue on ceiling.? My neighbor has shown me what appears to be smoke residue on...

My neighbor has shown me what appears to be smoke residue on her ceiling. It starts from around her boiler and fans out across the ceiling, getting lighter as it crosses the room. It have shown up within days gone by 4-5 days. It also does not appear on the ceiling wherever the ceiling beam are. PG&E came out and said that in attendance is not a carbon dioxide leak surrounded by her heater. She does not hold a fireplace, and has not have a fire. The only point that had gone on is that a contractor have come in and replaced adjectives the water radiator & water pipes inside her walls within the ultimate 2 weeks. This showed up about 1 week into this home repair. If you know what could be doing this, please permit me know. We are out of ideas.
My HE 3t washer kept flashing next to...
Answers:    Well, it could be 1 of 2 things:

1. It could be mold (growing surrounded by the ceiling and it is progressing across it). Wipe it with your finger or paw and see if it looks like mold. Mold can be a immensely serious problem

2. It could be dust-soot-grime etc. that got shook lose when the pipes & hose down heater be replaced. Wipe it with your finger or paw and see if it looks like dirt. Wash it adjectives off and see if it comes put money on.

If it comes back the dirt isn't done self spread around
or...........worse
It is MOLD because it just regrew where on earth you wiped it sour.
Need clog support or guidance: will drain-o...
If the contractor worked on the walls and made a lot of dust while the oven was running, conceivably the hot air convection lift some of that dust up and it drifted across the ceiling.