PRV 101: The Hidden Valve That Saves Water Heaters, Hoses, and Your Floors
If your faucets hiss when you open them, your toilet fill valves chatter, or your water heater’s relief pipe drips for “no reason,” you’re probably not haunted—you’re over-pressured. And the small part standing between “normal” and “mini flood” is a Pressure-Reducing Valve (PRV).
This guide explains what a PRV does, how high pressure quietly wears out everything in your home, the simple test you can run today, and the smart moment to repair or replace the valve. When you’re ready, A+ Drain Cleaning & Plumbing can check pressure, dial in the right settings, and protect your plumbing with a tune-up or a new PRV.
What a PRV is—and why Idaho homes need one
Municipal water pressure has to be strong enough to supply hydrants, multi-story buildings, and long street runs. That often means the pressure at your meter is higher than what your home’s fixtures and hoses are designed for. A PRV is installed on the main line (usually just after the shutoff where water enters the house) to step down street pressure to a safe, comfortable level for daily use.
Without a working PRV, excessive pressure:
Forces toilet fill valves and faucet cartridges to fail early.
Makes washing machine hoses balloon and rupture.
Causes your water heater’s TPR (temperature/pressure relief) valve to drip—sometimes constantly.
Turns tiny weeps at angle stops into full leaks.
Can make water hammer and hiss much worse.
Think of the PRV as a shock absorber for your plumbing. When it’s tired or misadjusted, the weakest part of your system pays the price.
Clear signs your pressure is too high
You don’t need a lab to spot these:
TPR drip at the water heater. The little pipe near your tank that occasionally discharges? High pressure can trigger that valve even when the heater itself is fine.
Chattering or whistling from toilet tanks as they fill.
Hoses that “thump” or bang when a washer stops filling (water hammer).
Leaking angle stops under sinks and at toilets—especially on newer braided lines that should be dry.
Sudden fixture failures (cartridges that die early, constant faucet drips after shutoff).
Super strong spray at one tap and then a noticeable pressure swing when another fixture turns on.
If two or more of those are happening, pressure deserves a look—before a hose or valve gives up completely.
The 5-minute PRV test you can do today
All you need is an inexpensive hose-bibb pressure gauge (hardware stores carry them). Here’s the drill:
Pick a test point: a front-yard hose spigot or the laundry faucet works great.
No water running: make sure nobody’s showering or washing dishes.
Read static pressure: screw on the gauge and open the spigot. Note the reading.
Read working pressure: turn on a second fixture (like a nearby sink) and watch the gauge.
Compare: Ideally, your home lives in a comfortable mid-range (many homeowners prefer roughly the 50s–60s). If you’re substantially above that, or if the pressure swings widely when fixtures open/close, your PRV may be due for adjustment or replacement.
Don’t have a convenient spigot? We can test at multiple points, including right at the PRV, and record both static and dynamic readings.
Why high pressure makes your water heater “leak”
Home plumbing built with a PRV is typically a closed system. When water heats up, it expands; if pressure is already high, that extra expansion has nowhere to go. Result: the heater’s TPR valve opens to relieve pressure, sending water down the discharge pipe. That constant dripping isn’t just wasteful—it can signal that your PRV is out of spec and your expansion tank might be under-charged or failing.
The fix:
Verify and adjust/replace the PRV.
Test/replace the expansion tank and match its air charge to your actual water pressure.
Service the heater (flush + anode check) while we’re there.
Add link when you publish: Water Heaters Service for the flush/TPR/expansion-tank workup.
Where to find your PRV (and what it looks like)
Indoors: mechanical room, crawlspace, or garage wall near where the main enters.
Outdoors: next to the foundation near the hose bib closest to the meter, sometimes in a covered box.
Appearance: a bell-shaped brass body with an adjustment screw/bolt on top and a union or flanged connections on each side.
If you see corrosion, green crust, or slow weeping at the seams, the valve has likely been at it for a while.
Adjust, repair, or replace? (Honest rules of thumb)
Adjust if: Your pressure is high but stable, the valve body is in good shape, and you just need to set it to a sensible range.
Repair if: The valve is newer but showing drift or minor internal wear; a rebuild kit (seat, spring, diaphragm) is available and cost-effective.
Replace if: Pressure swings wildly, adjustments don’t “hold,” the valve weeps externally, or it’s simply beyond its service life. Upgrading also ensures full-port flow for modern fixtures.
We’ll test first, then recommend the cheapest path that creates a long-term fix.
“My pressure is fine—why do I still get hammer and bounce?”
High pressure is only one piece. Two other factors can cause noise and fixture abuse:
Fast-closing valves (washers, ice makers, some faucets) can slam the column of water to a stop. If your arrestors are missing or water lines are unsecured, you’ll hear banging.
Thermal expansion from the water heater can spike pressure temporarily even with a PRV set well—another reason the expansion tank matters.
During a PRV visit we’ll also check for water-hammer arrestors, line strapping, and expansion control to keep things quiet.
The PRV + leak-detection connection
High pressure doesn’t just break things—it hides small leaks by pushing water into places you can’t see until it’s too late. Part of our PRV service is a quick meter test (watching the tiny flow indicator) with fixtures off. If the indicator spins when everything is “off,” there’s flow somewhere. From there, we can isolate toilets, heaters, softeners, and service lines to find the culprit.
Step-by-step: what we do on a PRV service call
Interview & walk-through – Symptoms, fixture behavior, hose/bib history, heater drip.
Pressure readings – Static and dynamic at 1–2 locations; record numbers.
Valve assessment – Check PRV type/age, test for drift, inspect for corrosion or weep.
Adjust or rebuild/replace – Based on findings and parts availability.
Expansion control check – Inspect expansion tank and match charge to new set pressure.
Water-heater sanity check – Verify TPR behavior, burner/electric function, and drain path.
Leak screen – Quick meter isolation to catch silent flow.
Proof & settings – Show you the before/after readings and leave the final set point in writing.
Most visits take under an hour; rebuilds/replacements may run longer if access is tight.
FAQs
What pressure should I set my home to?
There isn’t a single magic number—comfort, fixture type, and piping all play a role—though many homes feel great in the middle range most people prefer. We’ll test with fixtures running to confirm steady, comfortable flow after we set it.
How long does a PRV last?
It depends on water quality and usage. Some go a decade or more; others drift sooner. The behavior (drift, swings, leaks) tells the real story.
Can I just turn the screw until it “feels right”?
You can, but without a gauge, you’re guessing. We always set by the numbers and confirm dynamic behavior (pressure while water is flowing), not just static.
Why does my pressure spike randomly at night?
Municipal pressure can rise when neighborhood demand drops. A healthy PRV should buffer those swings.
Do I still need an expansion tank if I have a PRV?
Yes. A PRV creates a closed system; the expansion tank protects against heat-related pressure spikes from your water heater.
Prevention that pays for itself
Annual quick check: We can swing by to verify pressure and tweak as needed—especially smart after new fixtures or a water-heater swap.
Braided stainless: Replace rubber washer hoses and old supply lines; high pressure shreds them first.
Leak sensors: Under the heater, by the washer, and below kitchen/bath sinks.
Smart shutoff: Whole-home valves that close automatically on abnormal flow are cheap insurance for travelers and Airbnb owners.
Your 10-minute DIY pressure audit (printable)
Find the PRV location and note condition (corrosion, weep, age).
Measure static pressure at a hose bib (no water running).
Measure working pressure (open a second tap).
Check the water heater’s TPR discharge for drips.
Squeeze washer hoses—replace any soft or bulging lines.
Listen for toilet chatter or pipe banging.
If readings are high or swingy, schedule a PRV service visit.
Ready to protect your plumbing (and your floors)?
A healthy PRV keeps pressure sane, stops nuisance drips, and saves fixtures and hoses from early failure. If your heater’s relief line drips, toilets chatter, or you just saw big numbers on a gauge, let’s set your home up right.