Quick Answer:
If the shower spray is weak while the bathroom sink next to it runs strong, start by removing the showerhead and running the bare shower arm for 10–15 seconds. If the flow from the arm is strong, the showerhead is the likely problem — clean or replace it. If the arm flow is weak, the issue is deeper (valve cartridge, shutoff stops, or plumbing) and deserves closer inspection or a plumber.
Why This Happens
- Showerheads collect mineral deposits, sediment and small debris that restrict flow. That often affects the shower alone while nearby fixtures stay normal.
- Internal parts in the shower valve (cartridge or mixer) can wear, get clogged, or fail, reducing flow at that outlet only.
- Individual shutoff valves (angle stops) feeding the shower can be partially closed or clogged with sediment.
- Less common: a shared but isolated supply line problem to the shower, or debris from recent plumbing work.
Step-by-Step What to Do
1. Compare fixtures
Turn on the sink closest to the shower and note the flow. A strong sink flow means house pressure is fine and the problem is localized to the shower.
2. Remove the showerhead and test the bare arm
- Unscrew the showerhead by hand or with a cloth and adjustable wrench if needed.
- Run the shower from the bare shower arm for 10–15 seconds to flush any loose debris.
- Observe the flow:
- If the flow from the bare arm is strong: clean or replace the showerhead. Soak it in vinegar or follow the manufacturer’s cleaning steps, or buy a new head.
- If the flow from the bare arm is weak: proceed to check the valve and stops (next step).
3. Check the shower shutoff stops
- Locate the local shutoff(s) for the shower (often behind an access panel or under the sink). Open them fully if they are partially closed.
- If stops are open but flow is poor, they could be clogged with sediment. That usually requires more disassembly or a plumber.
4. Inspect the valve or cartridge
- If the arm flow was weak, the cartridge or valve inside the shower control may be clogged or failing.
- Replacing or cleaning a cartridge often restores flow, but it requires turning off water at home shutoffs and some plumbing experience.
5. What to try after reassembly
- Reattach a cleaned or new showerhead and test the spray pattern and flow.
- If the issue returns, repeat the arm test; persistent weak flow from the arm means the problem is inside the valve or supply line.
What Not to Do
- Don’t assume the whole house is low if only the shower is weak—test the shower arm first; if flow is weak there, a plumber is appropriate.
- Don’t force or hammer valve parts. That can break the valve body or create leaks.
- Don’t use concentrated acids or unknown chemical cleaners inside valves or cartridges — they can damage plastics and seals.
When to Call a Professional
- Flow from the bare shower arm is weak after flushing — this points to the valve, cartridge, or hidden supply blockage and usually needs a plumber.
- If you find corroded or stuck shutoff stops, or if accessing the valve requires cutting or removing wall material, call a pro.
- If you’re unsure how to shut off the home supply before working on the valve, call a plumber to avoid water damage.
- Related reads: see Tub spout pressure weak but sinks fine and Shower pressure suddenly dropped for other, similar scenarios.
Safety Notes
- Turn off the water supply to the bathroom or the whole house before removing valve cartridges or doing major work.
- Run the shower briefly after turning hot water back on to avoid scalding — test temperature with your hand at a safe distance.
- Wear eye protection when working under sinks or behind access panels; debris or pressurized water can cause injury.
Common Homeowner Questions
- Q: Why clean the showerhead first?
A: Most shower-only low-flow problems are caused by clogged heads, and cleaning is quick and inexpensive. - Q: Can I replace a cartridge myself?
A: Yes if you’re comfortable shutting off water and following the valve maker’s instructions; otherwise hire a plumber. - Q: Will a new showerhead always fix it?
A: No — if the bare arm flow is weak, a new head won’t help; the issue is upstream in the valve or supply.