Black smeary spots in bathtub

[ddton]

Hello all:

I had a Rheem natural gas water heater installed 3 years ago, to replace a rental tankless heater. This new heater has performed flawlessly. However, for about 5 months, every bath results in smeary black specs being deposited on the bathtub surface after it is drained. These spots do not clean up easily. As the tub is 8 feet from the water heater and draws the most hot water (my wife runs baths very hot) of any appliance in the house, I inspected the inlet strainers on the tub's faucet. Hot side was caked with black rubbery bits, cold side had no black debris. The tub's aerator also had a bit of black debris lodged in there as well. This problem is not appearing anywhere else in the house. I drained the water heater and strained it as it was dumped to an adjacent drain, no black debris, a disappointing finding. House is plumbed with pex + brass fittings, there are no flex hoses anywhere between the water heater and the tub. I know because I installed the tub during a reno a year ago.

I still suspect some black elastomer in the water heater is degrading. I used my magnifying lamp as I cleaned the tub's hot side strainer out. It had a rubbery texture, it was not greasy, just little black chunks. I confronted Rheem, they responded with a canned blurb about water chemistry.

Opinions anyone ? I think something in the water heater is failing, and it's under warranty. Any other tests/inspections I can do to conclude with high confidence the water heater is the culprit ? Any experience of water heater failures causing my symptoms ?

Sorry for lengthy post, want to give you decent background to work with. I'm really stuck on this, and need your help.
ddton

 

[Reach4]

Any braided supply lines to the tub?

 

[Sponsor]

 

[ddton]

Reach4, no braided lines feeding the tub. Only PEX/brass in the plumbing system. There are braided lines in the tub faucet itself, but these are AFTER the inlet strainers. When inspecting the strainers, I made note of their removal. Black rubbery debris was on the upstream side of the strainer. I concluded debris is not from faucet but from water heater. Faucet manufacturer Tenzo was contacted about this problem, they recommended strainer inspection. Tenzo says they've never heard of this problem before.

 

[Terry]

Braided lines to a water heater has been know to have some issues with black specks. If you have braided lines, you may want to change them out for corrugated copper or stainless steel.

 

[Phog]

There was another thread recently where the person was dealing with a similar problem.

https://terrylove.com/forums/index.php?threads/black-specks-only-in-hot-water.82767/

Synopsis; the person had black specks in only the hot water & at all hot fixtures. We all suspected the water heater flex connection lines but it ended up being a disintegrating plastic/rubber piece inside heat trap nipple.

 

[ddton]

phog, thanks for this. Pls see the pic I attached, is it the circular black disk that is the source of the problem being referred to ?

Assuming your answer is yes, some questions then:

1. Is this a problem affecting only the WH outlet side ? It makes sense that as hot water flows, rubber pieces are taken along for a ride to my tub. Also explains my finding that no black specs were found when I drained the WH. Specs seemed to be created when hot water flows out the WH outlet side, as it passes by rubber disc. Is my understanding correct ?
2. What is preferred solution ?
a. remove the nipple, take rubber out of the nipple, re-install and live with heat loss ?
b. replace nipple with another part that has heat trap feature, but no rubber ?
c. replace nipple with union that has no rubber, no heat trap and change my pex piping to do heat trap externally ?
d. something else ?

 

[Reach4]

If you pull the heat trap, I might change that out for one with the ball.

They sell those in pairs, color coded blue for cold and pink for hot.

Depending on your WH, the hot side nipple may have the anode on it. I think Rheem does not usually do this.

If the WH has a 1-1/16 hex, then that would be the anode.

 

[ddton]

Reach4, my Rheem has a separate anode connection, I read the manual and visually saw the hex head on the top of the tank.

I've read other threads that discourage the ball based trap, other problems were experienced. I've no experience myself, so will let others chime in.

thanks for quick response !
ddton

 

[Jadnashua]

There's an alternative to a heat trap in the nipple...make a big enough U-bend on the outlet of your hot water line to stop the convection. As the hot water tries to rise, it can't get past the U-bend, if it is big enough, but water flows fine once you open a faucet.