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.

  • Does it still happen? If so, a video might be helpful.
    – Tester101
    Commented Mar 3, 2016 at 2:39
  • You might have been seeing entrained air, which will sometimes look like gooey foam. But it's not clear how the air would get into the system, unless you're on a well.
    – Hot Licks
    Commented Mar 3, 2016 at 3:57
  • @HotLicks Would the gooey foam appearance be light or dark colored? When this has happened (two times in the last week), it looks like dark colored dirt is mixed with the water, but there is no evidence of dirt in the aerators or the water collected in the sinks. Commented Mar 5, 2016 at 22:02
  • @Tester101 It happened once more. I've updated the question. I didn't get a video, but if it happens again, I'll get one. Where should I post it? Commented Mar 5, 2016 at 22:03
  • When you get bursts of air running through the pipes it will pick up any sediment laying in the pipes, often of the form of rust or fine silt. This is material that was already in the pipes but was stirred up by the air. It can make the water appear quite "muddy" for a few seconds or a minute or two.
    – Hot Licks
    Commented Mar 5, 2016 at 22:59

1 Answer 1


So, it was something blocking the WH's outlet! Remove & disassemble the Aerators for additional evidence. But, definitely flush the tank or get a Plumber & sock him with that fiasco. It could be magnesium from the anode rod, an excess copper soldering flux interaction, plumbers grease (which shouldn't be anywhere), tank outlet gasket failure, tank lining deterioration or just sludge film from massive debris in the tank. But Hey, water pressure problem solved!!!

  • Thanks. Two questions (maybe you can add to your answer). 1. The WH outlets are on the top (2 of them, from what I can tell... don't know why); how does something flowing in the opposite direction as gravity get clogged? 2. Since it's working now, is it okay to ignore it for a few months (until access to the WH is easier)? Commented Mar 3, 2016 at 10:37
  • I should add that even though it looked like black goop was flowing out with the water, there was no evidence of anything at all in the stoppered sink which was collecting the water. Commented Mar 3, 2016 at 10:40
  • Yep, I got that, thus the film stuff. It make things look different coming out, but may only be noticed as a sheen or slick at the right light angle. You may have an invisible greasy ring in the sink now. The Tubs (bathing &/or laundry) are what you should've run. NO, flush that monkey out. Or, do you like that sludge on you & in you, now that you freed it to spread? Actually WH's fill from the bottom via Dip Tube so they don't cold the hot coming out & this also "tries" to blow sediments up into the flow. Everything floats down here, beep-beep Ritchie...Stephen King's IT, fyi.
    – Iggy
    Commented Mar 3, 2016 at 12:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.