Quick Answer:
If yesterday’s shower was normal and pressure dropped overnight, start by checking whether the change affects only that shower or other fixtures. If it’s just one shower, the head, arm, or local valve is the most likely cause. If multiple fixtures or both hot and cold are weaker, check the main supply, aerators, and any recent work on the system.
Why This Happens
- Mineral scale or debris can build up in a single shower head or the arm and block flow overnight.
- Local shutoff valves can shift or partially close, often after work or accidental contact.
- If several fixtures are affected, a change in main water pressure, a clogged main filter, or municipal work can be responsible.
- Problems on only the hot side often point to the water heater or a mixing valve.
- Recent plumbing work can leave debris in the lines that settles and reduces flow.
Step-by-Step What to Do
1. Compare to another fixture
- Run a faucet in another bathroom and the kitchen at the same time. Compare both hot and cold flow.
- If only the one shower is weak, proceed to local checks. If several fixtures are weak, skip ahead to the main-supply checks below.
2. Inspect the shower head and arm
- Turn the water off at the shower’s shutoff (if present) and remove the shower head. Look for mineral deposits, rubber washers, or debris inside the head and on the arm thread.
- Soak a clogged head in vinegar or use a small brush to clear mineral scale, then reattach and test.
- Also check the arm and visible pipe for blockages or kinks.
3. Check valves and diverters
- Operate the shower handle fully through hot and cold and the diverter to make sure parts aren’t stuck or partially closed.
- If you have separate shutoffs for the shower (behind an access panel), confirm they are fully open.
- If you recently had work done, see the note about Shower low pressure after plumbing repair for troubleshooting steps tied to repairs.
4. If multiple fixtures changed, check main pressure and aerators
- Remove aerators on sinks and rinse out debris. Aerators commonly collect sediment that reduces flow.
- Look for signs of low main pressure: municipal notices, neighbors with similar problems, or a sudden change at all faucets.
- Check the house main shutoff and any pressure regulator for obvious issues; if the regulator is failing, pressure will be low across the home.
5. If only hot water is weak
- Test whether cold is normal and hot is low; if so, the hot side is isolated. See the brief guide on Low pressure only on hot side at shower for common hot-side causes.
- Check the water heater for recent maintenance, anode issues, or sediment build-up that can reduce hot flow.
What Not to Do
- Don’t keep swapping fixtures blindly—verify whether the issue is local or whole-house first. Replacing parts without narrowing the cause wastes time and money.
- Don’t ignore multiple fixtures showing low pressure; if several fittings are affected, a plumber is appropriate rather than more DIY attempts.
When to Call a Professional
- Multiple fixtures lose pressure at once and basic checks (aerators, main shutoff) don’t help.
- You find a leak behind a wall, a failing pressure regulator, or suspect main-line damage.
- After trying the steps above you still have low pressure, or you’re uncomfortable working on valves or the heater.
Safety Notes
- Turn off the water at the appropriate shutoff before removing the shower head to avoid spray and potential water damage.
- Be careful when testing hot water—run it slowly to avoid scalding. Wear gloves if you work on hot plumbing parts.
- Use the right tools and protect finishes with a cloth when loosening chrome fittings to avoid damage.
Common Homeowner Questions
- Why did this happen suddenly? A small piece of debris, mineral scale shifting, or a valve moving can reduce flow quickly.
- Can I fix it myself? Yes, if it’s a single head or an aerator; remove and clean those first.
- When is it a plumber’s job? Call a plumber if multiple fixtures are affected, if you find leaks or damaged pipes, or if you can’t restore pressure after basic checks.