Quick Answer:
Pressure flickers on and off during showers are usually not a problem with the shower valve alone. Start by watching the whole water system: install a gauge with a max-needle to capture peak and low pressure readings, then correlate sudden drops to outside events (irrigation cycles, nearby storm interruptions, or PRV cycling). Use simple isolation checks to find whether the issue is upstream (municipal supply, curb/main work) or downstream (house plumbing, pressure regulator, or leaks).
Why This Happens
- Supply-side changes: municipal pressure can vary during peak demand or after nearby work. If someone has worked on the main or valve, you may see sudden shifts — see Pressure loss when main valve touched for related scenarios.
- Irrigation or timed systems: automatic sprinklers or large irrigation pumps can drop local pressure briefly during their cycles.
- Pressure regulator (PRV) cycling: a failing PRV can hunt or cycle, causing repeated ups and downs.
- Weather and storms: heavy storms or water main breaks in the area can cause temporary supply instability.
- Partial leaks or partial blockages: intermittent or slow leaks on the supply side can cause pressure to drop when demand changes.
- Recent utility work: curb stop or meter work can leave debris or change system behavior — see Pressure failure after curb stop work for more context.
Step-by-Step What to Do
1. Record when it happens
Note exact times the flicker happens: during showers, when sprinklers run, during storms, or after someone else uses water. Time correlation is the quickest clue.
2. Install a gauge with a max-needle
- Buy a simple water pressure gauge that has a max (peak) needle. The max-needle stays at the highest pressure reached and helps show brief spikes or dips you might miss.
- Install the gauge on an accessible threaded outdoor spigot or washing machine outlet using appropriate adapters. Leave it in place while you run a shower or wait through a suspected trigger (sprinklers, storm).
- Record the normal reading, the peak, and the low. The max-needle tells you if pressure spikes then falls quickly.
3. Correlate pressure drops to triggers
- Run the shower with the gauge connected and note whether drops line up with sprinkler cycles or other house equipment starting.
- Watch during or after storms. If pressure dips only during storms, the issue is likely supply-side and temporary.
- If a PRV cycles when pressure falls and recovers regularly, that points to a regulator problem.
4. Isolate upstream vs downstream causes
- Ask a neighbor whether they see the same flicker. If they do, it’s upstream (municipal or main).
- If possible, close your house shutoff valve to test: if pressure on the meter side still drops, the cause is upstream. If pressure stabilizes after closing the house shutoff, the issue is inside your plumbing.
- Do not try to operate curb stops or meter hardware if you’re unsure; if the isolation requires work on the public side, contact your water utility.
5. Check visible components
- Inspect the PRV (if present) and the pressure tank on wells: look for leaks, corrosion, or obvious damage.
- Listen for running water or damp spots that could indicate a leak activating under certain loads.
What Not to Do
- Do not assume intermittent loss is a fixture issue—track system-wide behavior first.
- Do not repeatedly run fixtures to “flush” the problem without gathering data; that wastes water and hides patterns.
- Do not attempt to force or remove curb stops, meter seals, or municipal equipment; that can be illegal and dangerous.
- Do not immediately replace fixtures or shower cartridges before confirming the pressure pattern with a gauge and isolation tests.
When to Call a Professional
- If the gauge and isolation tests point to upstream issues but your neighbor reports the same problem, call your water utility first.
- Call a licensed plumber if you cannot isolate the problem, if a PRV appears to be failing, or if you find signs of a leak you cannot locate or stop.
- Call an emergency service for active, large leaks, sudden loss of pressure across the whole house, or if you notice structural water damage.
Safety Notes
- Avoid tampering with utility-owned equipment (meter, curb stop, mains). Contact your utility for public-side concerns.
- Shutting off the main valve can interrupt fire-suppression devices or sprinklers—warn occupants first.
- When installing a gauge, use the right adapter and hand tools; do not over-tighten or use power tools that can damage fittings.
- If you see exposed wiring near wet areas or electrical gear getting wet, stop and call a professional electrician or plumber.
Common Homeowner Questions
- Is the shower valve the likely cause?
Not usually; intermittent, system-wide drops are more often supply or PRV related. - How long should I log readings?
At least one full day that includes peak uses (morning, irrigation run times, and evening showers). - Will a plumber charge to diagnose?
Most charge a diagnostic fee; gathering your gauge logs first can reduce time and cost.
Related Articles
If you’re troubleshooting a similar symptom, these guides may help:
For the full directory, see Intermittent Pressure Loss Events.