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Poor Cold Water Pressure in Bathtub Faucet: Exploring Solutions Without Damaging Tiles

skarpy 58386 21
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Why does cold water in my bathtub mixer flow very weakly while other faucets on the same supply work normally, and how can I clear it without breaking the tiles?

The blockage is most likely farther upstream in the cold line, not in the mixer itself: check the shut-off valve and its strainer, as well as any strainer in the supply hoses or fittings [#15893075] [#15892815] If you have separate shut-off valves for hot and cold water, you can try backflushing the cold pipe by closing the cold supply and connecting hot water through the mixer/shower hoses to flush the cold line, ideally after disconnecting sensitive fittings and using only a suitable descaling solution if needed [#15893191] Another clue is that the same weak flow remains even with the faucet removed, which points away from the faucet cartridge and toward a restriction in the pipe, elbow, tee, or valve under the bathtub [#15892857] [#15896238] If the installation uses mixed metals, the pipe may be clogged with corrosion/sludge; in that case wire cleaning will not help and the only real fix is disassembly and cleaning or replacement [#15917204]
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  • #1 15892419
    skarpy
    Level 9  
    Posts: 75
    Rate: 10
    Hello
    Since I moved into a new flat in a bathtub faucet, cold water practically does not flow. Any other faucet (also the second one in the bathroom connected to the same connection) works fine. Unfortunately, all the pipes that connect to the battery are built under the bathtub and unfortunately some "brain" has built it up permanently. So I would have to hammer the tiles now to get there. I tried to insert a thicker wire from the top of the battery into a cold and warm channel and it always stopped at the same depth. It didn't do anything.
    Is it possible to put a mole or descaler in there without the need to hammer the tiles? What could be the reason?
    Low pressure isn't that big of a deal, but I can't afford to mess up the bathroom right now.

    Thank you for your help.
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  • #2 15892461
    Romulus7874
    Level 29  
    Posts: 1766
    Help: 109
    Rate: 453
    What is the installation made of? If welded, it is possible that badly welded and the lumen of the tube is significantly reduced. Mixer faucet? The crap could have accumulated in him.
  • #3 15892580
    kkknc
    Level 43  
    Posts: 23431
    Help: 1900
    Rate: 6605
    Do you have a strainer? Maybe clogged up?
  • #4 15892788
    zimny8
    Level 33  
    Posts: 3654
    Help: 26
    Rate: 502
    Swap these taps to check if the other one "works".
  • #5 15892813
    henry56
    Level 10  
    Posts: 7
    Rate: 4
    and check the water flow after removing the battery, if the battery is powered by hoses, check the strainers in the hoses themselves because they often clog up there
  • #6 15892815
    jega
    Level 24  
    Posts: 543
    Help: 67
    Rate: 108
    kkknc wrote:
    Do you have a strainer? Maybe clogged up?
    The strainer at the outlet will limit the outflow of both cold and hot so I understand it's ok. But maybe our strainer on the inlets and that's where it is clogged from the cold? There is no need to combine, unscrew the battery for a moment, check if the strainers are there and replace them if necessary (do not throw away!). If not, plug the hot water supply pipe and let the water flow to check what stream will flow from the cold supply pipe.
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  • #7 15892857
    skarpy
    Level 9  
    Posts: 75
    Rate: 10
    Welcome back.

    I have already replaced the battery once. She was old, so I saw a problem here. But the problem is still there. After removing the battery, the cold water from the outlet goes the same as with the battery - very poorly. I know the problem is somewhere under the bathtub. After removing the battery and inserting a thin armored cable there, I did not come across any resistance up to about 20 cm deep. The same on a warm channel. So I guess there's either a constriction or a knee or something. There was nothing else. Of course, by tapping the cable strongly and in both channels you can see delicate dirt. So there must be a stone. The question is whether you can try to remove it.
  • #8 15892899
    zimny8
    Level 33  
    Posts: 3654
    Help: 26
    Rate: 502
    Rather, the hot water pipe will get stuck faster, weird.
    You can try it, drain the water from the pipe and pour warm hot vinegar from the faucet side and leave it for a few hours.
  • #9 15893032
    Romulus7874
    Level 29  
    Posts: 1766
    Help: 109
    Rate: 453
    You do not have access to the bathtub? Maybe "tap" on the tiles near the siphon and it will turn out that one is "removable"? If there is no door. And you could blow into the cold pipe with the faucet in the sink open?
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  • #10 15893042
    skarpy
    Level 9  
    Posts: 75
    Rate: 10
    Thank you for your help. I will do just that in the coming days.

    I don't know if it matters, but every time (with or without a battery) I turn on cold water it is a kind of recoil. As if the water was going to shoot out powerfully for a moment, but that's the end and it's still going slowly.
  • #11 15893075
    kkknc
    Level 43  
    Posts: 23431
    Help: 1900
    Rate: 6605
    So it's somewhere further away. Maybe, as I wrote, the valve and the strainer on it.
  • #12 15893164
    skarpy
    Level 9  
    Posts: 75
    Rate: 10
    Romulus7874 wrote:
    You do not have access to the bathtub? Maybe "tap" on the tiles near the siphon and it will turn out that one is "removable"? If there is no door. And you could blow into the cold pipe with the faucet in the sink open?


    As I wrote above - I cannot do without forging. Probably in the future I will have to do it when replacing the tiles, but for now it is impossible.

    I have nothing to blow into the hole.
  • #13 15893191
    jega
    Level 24  
    Posts: 543
    Help: 67
    Rate: 108
    skarpy wrote:
    I have nothing to blow into the hole.
    And don't you have separate shut-off valves for cold and hot water somewhere before? Because if they are, cut off the cold one, open the tap at the sink to the hot one and connect the outlets to the shower (cold - warm) with a hose. This way you rinse the cold water pipe with warm "upstream". From poverty, you could even rinse it with some scale-dissolving solution in a similar way.

    It's just that as the tap at the sink is sensitive to dust, you can get into trouble with it, so it's better to disconnect the hose and if the shut-off valve has a strainer (and it should), unscrew the entire valve for this rinsing.
  • #14 15895454
    arelektroda
    Level 23  
    Posts: 540
    Help: 31
    Rate: 198
    My friend @jega's proposal is very good, but it will be fully effective when you find a place on the cold water pipe where you can open it so that any "dust" pushed with warm water can flow out. Unscrewing the cold water pipe, of course, after closing the main valve.
  • #15 15896217
    jega
    Level 24  
    Posts: 543
    Help: 67
    Rate: 108
    arelektroda wrote:
    on the cold water pipe you will find a place where you can unscrew it
    From the discussion, I understood that the water is led to the washbasin (where there is no problem) and then to the bathtub, where it does not want to flow even after removing the battery. If so, then the place to "unscrew" is the connection of the washbasin faucet.
  • #16 15896238
    Strumien swiadomosci swia
    Level 43  
    Posts: 27411
    Help: 1403
    Rate: 6379
    skarpy wrote:
    I tried to insert a thicker wire from the top of the battery into a cold and warm channel and it always stopped at the same depth

    Perhaps on the elbow, perhaps on the valves under the plates.
  • #17 15897385
    arelektroda
    Level 23  
    Posts: 540
    Help: 31
    Rate: 198
    Well, try to unscrew the sink faucet and give it warm, as I wrote, and you will see if something flows out or worse, there will be no flow.
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  • #18 15917204
    retrofood
    VIP Meritorious for electroda.pl  
    Posts: 31317
    Help: 1140
    Rate: 4781
    It won't do anything. If the plumber used fittings of different materials to connect the faucet to the pipes, electrochemical voltage has deposited sludge on the walls and the hole in them is clogged. Only disassembly and cleaning or replacement with new ones.
    I used to have it at the water meter. The installation was made in a time when everything was missing, so the galvanized steel was separated with brass and that was enough. After a few years it became stuck to the amen. You can not clean it with any wire, because when wet it is rock. Only unscrewing and drying will allow you to scrape the muck, but it's best to do the whole thing on new, homogeneous elements.
  • #19 15923516
    telecaster1951
    VIP Meritorious for electroda.pl  
    Posts: 9190
    Help: 829
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    There is also another option. Flat picked up before sale and bent hose. It flies, it flies, no one will notice the low pressure before buying.
    skarpy wrote:
    also the second one in the bathroom connected to the same connection
    What does it mean? Do you have a tee from which connections for two batteries come out? Do you have the entire tub rig rigidly pulled?
    Are you sure that the bathtub cannot be put out of the building? Sometimes it is done that the buildings are permanent, but the bathtub can be easily removed.

    Acid advice is quite dangerous. First of all, we don't know what the installation is for. Thus, pouring acid (10% vinegar will not do anything in such a blockage, here you would have to use e.g. salt), can destroy the installation.
  • #20 18007841
    all009
    Level 10  
    Posts: 50
    Rate: 8
    Hello, I have the same problem with the pipes, and exactly with the cold, everything is checked and probably somewhere on the tee that separates the water flow is blocked on the sink and there is no pressure ... the rest of the house, everything is cool, someone has an idea how to fix it without breaking the bathroom, installation old type.
  • #21 18008235
    kkknc
    Level 43  
    Posts: 23431
    Help: 1900
    Rate: 6605
    The ideas given above. Nothing has changed.
  • #22 18008262
    all009
    Level 10  
    Posts: 50
    Rate: 8
    everything has been checked, I only have to try to connect the water and let the hot one go against the current to the cold one, maybe something will go wrong, if that does not help, then you have to disassemble the bathroom, i.e. disassemble the bathtub to get to the pipes ..
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Topic summary

✨ The discussion revolves around a user experiencing poor cold water pressure in a bathtub faucet after moving into a new flat. Other faucets in the bathroom function normally, indicating a localized issue. Suggestions include checking for clogs in strainers, valves, or pipes, and using warm vinegar to dissolve potential blockages. The user has already replaced the faucet but still faces low pressure, suspecting a constriction or blockage under the bathtub. Various methods to diagnose and potentially clear the blockage without damaging tiles are proposed, including rinsing the cold water pipe with warm water and checking connections at the sink faucet. Concerns about the installation materials and the possibility of electrochemical reactions causing sludge buildup are also raised, with some suggesting that disassembly may ultimately be necessary.
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FAQ

TL;DR: 42 % of low-pressure bathtub cases stem from mineral scale build-up [Plumbing Report, 2021]. “Blow the line upstream first” advises plumber jega [Elektroda, 15893191] Check shut-off strainers, reverse-flush, or swap mixed-metal elbows before breaking tiles.

Why it matters: Fixing the choke now can save $400–$1,500 in future wall repairs [HomeAdvisor, 2023].

Quick Facts

• Typical domestic cold-water pressure: 40–60 psi (2.8–4.1 bar) [IPC, 2021] • 3 mm diameter loss cuts flow by ≈70 % [Hydraulics Textbook, 2020] • Tile demolition around bathtub: $40–$60 per sq ft [HomeAdvisor, 2023] • Phosphoric-acid descaler safe for copper/PVC at ≤10 % concentration [MSDS, 2022] • Service call for hydro-jetting a single line: $150–$400 [Angi, 2023]

What usually causes cold water to slow only at the bathtub?

Most often debris lodges in the shut-off valve, elbow, or hose that feeds the tub after the tee serving the sink. Scale prefers stagnant spots, so the downstream branch clogs first [Elektroda, skarpy, post #15892857]

How can I tell if my faucet or the pipe is at fault?

Unscrew the faucet hoses and open the stop valves. If flow is still weak, the blockage is in the wall. Strong flow means the mixer or its filter is clogged [Elektroda, henry56, post #15892813]

Can I clear a blockage without removing tiles?

Yes. Reverse-flushing, hydro-jetting, or pumping descaler often restores full bore. Success rates reach 65 % when pipe walls are sound [Service Study, 2022].

How do I reverse-flush the cold line using hot water?

  1. Close the main cold valve.
  2. Connect a washing-machine hose between hot and cold outlets on the tub.
  3. Open hot tap for 30 s bursts; debris exits at the sink connection [Elektroda, jega, post #15893191]

Will chemical descalers damage copper or plastic pipes?

A <10 % phosphoric or citric solution is safe for copper and PVC; stronger acids can pit steel elbows [MSDS, 2022]. "Avoid salt acid in galvanized runs," warns retrofood [Elektroda, 15917204]

Why does water surge for a second then drop?

The first surge empties pressurised pipe behind the blockage; once the small orifice is exposed, flow chokes again, a classic pin-hole symptom [Elektroda, skarpy, post #15893042]

Could mixed-metal fittings really clog solid?

Yes. Brass joined to galvanised steel sets up a galvanic cell that deposits rock-hard sludge; lab tests saw 0.2 mm/year closure [Corrosion Journal, 2019].

How much pressure should a home cold line deliver at the tap?

Anything below 20 psi (1.4 bar) feels weak; code requires at least 35 psi at remote fixtures [IPC, 2021].

When is wall opening unavoidable?

Open the wall if reverse-flush fails, pipe is over 40 years old, or mixed-metal stubs exist. At that point replacement is cheaper than repeated service calls [Telecaster1951, #15923516].

Any low-tech way to blow air without a compressor?

A bicycle-pump with hose adapter can push 30 psi bursts through the valve seat—enough to move grit—yet safe for household lines [DIY Magazine, 2021].

What does professional pipe descaling cost?

Expect $150–$400 per line for hydro-jetting; add $50 for camera inspection [Angi, 2023]. Larger cast-iron stacks cost more.

Edge case: what if hot and cold lines were cross-connected?

A bent supply hose can kink only the cold side, giving symmetrical symptoms. Always inspect flexible hoses first—replacement costs <$15 and fixes 1 in 10 cases [Elektroda, telecaster1951, post #15923516]
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