Reduced Water Flow in Single Bathtub Faucet

[GregoryH]

This is stumping me, maybe someone has an idea.

In our one year old house in Texas, slab foundation, PEX throughout. The cold water faucet on the bathtub is the *only* faucet experiencing the problem.

*Open the faucet.
*Water comes out at full pressure for about 2 seconds, then drops to just a little more than a trickle (maybe 1/10th of the normal flow/pressure).
*Just as the flow drops, there is a distinct "thump" or clunk sound and feel in the faucet handle (but that could be happening upstream).
*Wait an hour or more and the same thing happens again (normal flow for 2 seconds), but if you immediately turn it off and back on, the flow comes out slowly. So something *reverts* back over time.

What I tried - (Already determined the ceramic disk-valve is clean)
*Turned off water.
*I removed the valve entirely.
*Put in a 2 ft. piece of clear, 1" O.D. vinyl tubing down inside the valve body, then pointed the other end down into the tub.
*Turned on main water valve (had someone hold the hose in the valve body), water still comes out at reduced flow with no valve in the valve body.

So:
*Water comes out for only a moment at full pressure, then reduces to a very low pressure flow. This is accompanied by a thud on the line (but I'm not clear where that is taking place). It will 'reset' itself after an hour or more. Almost like a pebble is caught somewhere upstream. I had hoped using the vinyl tubing would allow the obstruction to clear out but no dice (if it's a stone).

Thoughts? A pebble from construction or when they connected up to the main? An airlock?

Thanks for suggestions.

Edit: Well someone mentioned to me airlock so I tried the method of blocking the faucet spout with my hand and opening both faucets, which blows out the bubble? Seemed to work instantly, but only for a short time. Problem still present.

 

[Reach4]

Problem will probably be some kind of balancer or mixer. Those can control the amount of hot or cold that gets mixed.

Is there access to the valves from the back via an access panel? Sometimes there is a closet with a panel. You may have to lift out shelves to get in there.

Was the problem there when you moved in, or is this a new symptom? I am not a pro. A photo of what you can see from the back or front can often give people info about what you have. To upload make it 800 pixels or less and 200 KB or less. Or post a link to a picture.

 

[Sponsor]

 

[GregoryH]

Problem will probably be some kind of balancer or mixer. Those can control the amount of hot or cold that gets mixed.

Is there access to the valves from the back via an access panel? Sometimes there is a closet with a panel. You may have to lift out shelves to get in there.

Was the problem there when you moved in, or is this a new symptom? I am not a pro. A photo of what you can see from the back or front can often give people info about what you have. To upload make it 800 pixels or less and 200 KB or less. Or post a link to a picture.

Problem was present from the first day of move in. And to my frustration, there are zero access points. Meaning no mixing valves or rear panels to the tub (tub faucet is butted up against a shower stall - so no access). I meant no mixing valves anywhere on the premises.

I tried the airlock technique which seemed worked for a a minute or two. Went back and everything the same again.

 

[GregoryH]

Faucet image. By the way, the supply lines come directly out of the slab foundation, so there's only roughly 12" of line coming straight up. No other access in these new houses for the water. The main shut off by the street and a really hard to reach shut-off up by the house. A really poor design.

 

[GregoryH]

So I found a thread about airlock suggesting you drain the entire system (cold side in this case), then with all cold valves slightly open (bleed the system?), turn on the main feed until water is running throughout. So for now, that seems to have solved the problem.

 

[hj]

"AIR block" was NOT the problem, regardless of what it took to cure it. The valve may have been partially closed, before you turned it off and then on again.