I have been dealing with some hot water pressure issues. See Should hot water pressure be reduced after hot water is used?
Today, hot water pressure reduced so much it was impossible to shower.
In that other Q/A, it was recommended that I purge the hot water heater.
Access to the hot water heater is not trivial, so I decided to run all the sink faucets on full-hot to see what would happen.
Pressure was very low, but water was flowing through all the faucets.
Then, suddenly, all the faucets started flowing at full throttle.
I took a look at the water coming out, and it looked like gobs of dirt were flowing out with the hot water. But that seemed odd, as there are aerators on all the faucets.
After running for about 3 minutes, there was still large dark blobs coming out of the faucets. There was no specific timing, but about 2-3 blobs roughly every 5 seconds.
I then put a stopper in one of the sinks and turned off the rest of the sinks. The blobs continued to appear, but the sink filled with what looks like clean water.
After about 10 minutes of running the water, there were no more dark blobs.
What was I seeing? I thought it was sediment from the water heater, but now I'm thinking that perhaps large air pockets look like dirt when passing through an aerator. Or perhaps it's something else?
Bonus: What would have caused this issue? (If it's best to have this "bonus" as a separate question, just let me know, and I'll create another one.)
UPDATE: I'm working on getting to the water heater to drain it, but I have some heavy equipment blocking access, so it's going to be an endeavor. In the meantime, everything was working fine, until today. Hot water pressure suddenly dropped again. I don't have a non-regulated sink, so I ran 3 bathroom sink faucets on full-hot simultaneously, first plugging the sinks. After about 30 seconds, I heard a loud CLUNK in the pipes, and then hot water started flowing freely.
It looked like black gunk was coming out of the faucets, but a visual inspection of the water (trapped in the sinks) and the sinks themselves shows no evidence of anything, not even a film. I did see one tiny spec (less than 1 mm) of green metal (oxidized copper, perhaps), but that could just be from an aerator or the stopper. I took off one of the aerators, and there was no evidence of anything.
The source of cold water is municipal water, not well water.