Quick Answer:
If sinks and toilets have normal pressure but the shower feels weak, start by removing the showerhead and testing the flow from the bare shower arm. If the flow is strong from the arm, the showerhead is clogged or restricted. If the flow is still weak, the problem is likely the shower valve, cartridge, or the supply to that branch of plumbing.
Why This Happens
- Mineral deposits or debris often build up inside a showerhead or its removable flow restrictor, cutting flow to the shower but not to other fixtures.
- Shower valves and cartridges wear or become blocked over time. A partially blocked cartridge can reduce flow only to that fixture.
- Diverter valves (on tub/shower combos) or a malfunctioning pressure-balancing device can restrict flow to the shower outlet.
- Local shutoff valves serving the shower may be partially closed, or an isolated supply line can be restricted by sediment.
Step-by-Step What to Do
1. Confirm it’s only the shower
- Run a sink and the toilet. If they run normally, you can concentrate on the shower plumbing instead of the whole house supply.
2. Remove and test the showerhead
- Unscrew the showerhead by hand or with a wrench protected by a rag. Watch for old thread tape or corrosion.
- Turn the shower on while the showerhead is off and observe the flow from the bare arm. If the flow is strong from the arm, the head is restricted.
- If the flow from the arm is weak, proceed to the valve and supply checks below.
3. Clean or replace a restricted showerhead
- Soak the showerhead in white vinegar for an hour to dissolve mineral buildup, or remove and soak the removable parts. Brush out deposits and test again.
- Check for a plastic flow restrictor inside the head. Removing or replacing it can restore flow, but be aware of local regulations about maximum flow rates.
- If cleaning doesn’t help, replace the head — it’s usually inexpensive and easy.
4. Check diverter and tub spout issues
- If you have a tub/shower diverter, operate it and listen for a change in flow. A stuck or worn diverter can divert water away from the showerhead. Inspect or replace the diverter as needed.
- Also check the tub spout for reduced flow; it can indicate a shared problem. See **Tub spout pressure weak but sinks fine** for more on tub-related issues.
5. Inspect the shower valve and cartridge
- Turn off the water at the fixture shutoffs or the main before working on the valve.
- Remove the trim and handle to access the cartridge. Look for buildup, corrosion, or broken parts. Flushing the valve briefly with the water on (with the cartridge removed) can clear debris, but only do this if you are comfortable and the shutoff is in place.
- Cartridge kits and replacement instructions vary by brand. If the cartridge is worn or cleaning doesn’t help, replacement often fixes weak shower-only pressure.
6. Check local shutoffs and supply lines
- Make sure any in-line shutoffs that feed the shower are fully open.
- If the supply line has sediment or the pipe is narrowed, you may see reduced flow even with the head removed. Persistent weak flow after the head is off is a sign to focus on the valve or supply piping.
What Not to Do
- Don’t assume low shower pressure means the whole house is affected; if only the shower is weak, a valve or cartridge issue is more likely.
- Don’t force parts. Forcing a stuck cartridge or trim screw can break components and cause leaks.
- Don’t pour harsh drain chemicals into the shower to try to clear a mechanical restriction inside the valve; they won’t help and can damage finishes and seals.
- Don’t overtighten fittings or use metal-on-metal contact without a rag or tape on tools—this can strip finish or threads.
When to Call a Professional
- Flow from the bare shower arm is weak: this points to the valve or supply and usually requires a plumber.
- There are leaks when you open the valve, or if removing the cartridge looks complex for your skill level.
- The shutoff for the shower is inaccessible or the main shutoff is hard to operate safely.
- The issue started suddenly and affects multiple fixtures unexpectedly; consult a plumber to check pressure regulators or main supply problems. If you noticed a sudden change, check **Shower pressure suddenly dropped** for related troubleshooting steps.
Safety Notes
- Always turn off water at the fixture shutoffs or main before removing internal valve parts. Open a faucet to relieve pressure before disassembly.
- Use basic eye protection when flushing lines or clearing debris. Mineral particles can spray out when pressure is applied.
- If you are unsure how to reassemble trim or how to stop a leak, stop and call a licensed plumber. Incorrect installation can cause water damage.
Common Homeowner Questions
- Will cleaning the showerhead fix weak shower pressure?
Often yes — if the flow is strong from the bare arm, cleaning or replacing the head usually fixes it. - How hard is it to replace a shower cartridge?
Hardness varies by brand; basic DIYers can do it, but tight spaces, corroded parts, or unclear shutoffs are reasons to hire a plumber. - Can a clogged aerator on a sink cause shower problems?
No — a clogged sink aerator won’t affect the shower. If only the shower is weak, focus on the showerhead, diverter, or valve.