Shower pressure varies daily

Shower pressure varying day-to-day with the same handle setting.

Quick Answer:

Daily variation in shower pressure can come from the water company, a pressure-reducing valve (PRV), daytime demand in your neighborhood, or intermittent restriction inside the plumbing or shower valve. Start by measuring pressure at an exterior hose bib or laundry tap at different times with a simple pressure gauge. If readings rise and fall across the whole house, the PRV or supply is likely the cause; if only the shower changes, inspect the shower valve and cartridge.

Why This Happens

  • Municipal supply fluctuates by time of day. Peak use in mornings and evenings lowers system pressure.
  • A failing or set PRV (pressure-reducing valve) can drift or stick, causing intermittent swings.
  • Partial blockages from sediment or mineral build-up can open and close with flow or temperature changes.
  • Shower valve cartridges, diverters, or thermostatic mixers can work intermittently and reduce flow only at certain times or when other fixtures run.
  • Leaks or shared piping loads in the house can change pressure when other appliances run.

Step-by-Step What to Do

Step 1 — Check other fixtures

  • Turn on a tap in the kitchen or a laundry basin at the same time you test the shower. If those taps show the same variation, the problem is likely system-wide.

Step 2 — Measure water pressure at different times

  • Attach a simple pressure gauge to an outdoor hose bib or a laundry tap if available. Record readings morning, midday, and evening over a few days. This tells you whether pressure actually varies or if it is only perceived at certain times.
  • If pressure at the bib swings with the shower, the PRV or supply is probably the real driver.

Step 3 — Compare whole-house vs single-fixture behavior

  • If only the shower loses pressure, isolate the shower: turn off other water-using appliances and retest.
  • If the whole house drops, focus on the main shutoff, PRV, or municipal notice of reduced supply.

Step 4 — Inspect the shower valve and hardware

  • Remove the shower head and run the valve to see if flow improves. Clean screens and check for mineral build-up.
  • If you recently serviced the valve, consult guidance for issues like a mis-seated cartridge — consider the note about Low pressure after changing cartridge.
  • Check the tub/shower diverter if pressure changes when the tub is used; see the guidance on Shower pressure weak only when tub used.

Step 5 — Look for timing and external causes

  • Ask neighbors or check local notices for scheduled water main work or known outages. Municipal work or firefighting demands can cause temporary drops.

Step 6 — If you suspect the PRV or main supply

  • Confirm whole-house pressure swings with the gauge. A PRV that sticks or loses adjustment will cause the pattern you describe.
  • Document readings and times before contacting a plumber — this information speeds diagnosis.

What Not to Do

  • Don’t dismiss frequent daily variation—measure pressure at another tap to confirm whether it’s just the shower.
  • If fluctuations are system-wide, a plumber is appropriate; don’t ignore a failing PRV or a main-supply issue.
  • Don’t randomly replace parts (like the cartridge or PRV) without measurements or diagnosis — that can waste money and miss the real cause.
  • Don’t attempt major adjustments to a PRV or the main supply without experience; it can cause sudden high pressure that damages fixtures.

When to Call a Professional

  • Pressure swings affect multiple fixtures or the pressure gauge shows wide variation over time.
  • You suspect a failing PRV, a hidden leak, or a problem with the main supply line.
  • Your testing and simple cleaning don’t restore consistent pressure or you’re unsure how to proceed safely.

Safety Notes

  • Turn off the main water before working inside valves or cutting pipes. If you are not comfortable, stop and call a pro.
  • Be cautious with hot water when testing valves; open cold first and avoid scalding.
  • Leave PRV adjustments and main-line work to licensed plumbers unless you have proper tools and experience.

Common Homeowner Questions

  • Can I test pressure myself? Yes — a simple garden-hose gauge on a hose bib or laundry tap gives useful readings.
  • How long should I record readings? A few days with morning, midday, and evening checks is usually enough to spot a pattern.
  • Will replacing the shower head fix it? Only if the shower head is the restriction; test other fixtures and use a gauge before replacing parts.

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