PRV Failure -- High Water Pressure
Updated February 20, 2026
Failing PRV lets dangerously high pressure into the house. Bursts supply lines, damages appliances, causes hammer, shortens fixture life, leaks everywhere. Normal is 40-60 PSI. Above 80 is dangerous and needs immediate attention.
Overview
Bell-shaped brass fitting on the main line. Reduces municipal pressure (80-150+ PSI) to safe residential levels (40-60 PSI). When it fails, full pressure enters unchecked. Above 80 PSI stresses every connection, fixture, valve, and appliance. Accelerates cartridge and fill valve wear, causes hammer, dramatically increases burst risk. PRVs last 7-12 years before the spring and diaphragm degrade.
Symptoms
- Aggressive spray, excessive splashing, hard to control the stream -- pressure noticeably stronger than normal
- Water hammer when faucets or appliances shut off -- high pressure amplifies hydraulic shock
- Toilets running or fill valves humming -- pressure pushes past the seal
- Faucets and valves developing leaks more frequently -- accelerated wear on cartridges, O-rings, seals
- Water heater T&P valve dripping or discharging -- safety response to excess pressure
- Pressure gauge above 80 PSI at any hose bib confirms it
Common Causes
- Spring and diaphragm failure -- weakens over 7-12 years. Diaphragm cracks, hardens, or tears. Gradual, not sudden. Allows higher and higher pressure through.
- Sediment or mineral buildup -- hard water deposits prevent the diaphragm from moving freely. Valve sticks open (full pressure) or becomes erratic.
- Incorrect adjustment -- someone turned the screw clockwise (increases pressure) without knowing what it does. Common after plumbing work.
- Past lifespan -- not designed to last the life of the home. 20-30 year old original PRV is almost certainly not regulating effectively.
- Thermal expansion in a closed system -- backflow preventer creates a closed system. Heated water expands with nowhere to go. Pressure spikes over 100 PSI even with a working PRV. Fix is an expansion tank, not a PRV adjustment.
What You'll Need
How to Fix It
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Test the Water Pressure
Pressure gauge on a hose bib ($10-15). All other fixtures closed. Normal: 40-60 PSI. Up to 80 acceptable but high. Above 80 needs correction. Test at different times -- often highest late at night when demand is lowest.
Tip: Test with the heater off and then heating. Normal when off, spikes when heating? Thermal expansion, not PRV failure. Expansion tank is the fix. -
Try Adjusting the PRV
Above 60? Try adjusting first. Bell-shaped brass fitting on the main line. Counterclockwise on the adjustment bolt, quarter turns. Check pressure inside after each turn. Goal: 50-60 PSI. No effect on the reading? Internal components have failed, needs replacement.
Warning: Do not go below 40 PSI. Poor flow at upper floors, sprinklers will not function, some appliances (tankless heaters) require minimum pressure to activate. -
Replace the PRV (Professional Recommended)
Adjusting does not work? Replacement. Main water off (meter or curb stop), old PRV cut or unscrewed, new one in. Same size as the main line (typically 3/4 inch). Set to 50-60 PSI. Involves soldering, threading, or push-fit depending on pipe material. Typically a plumber job.
Tip: Ask for a Watts or Zurn with a downstream gauge port. Permanently install a small gauge for easy monitoring without needing a hose bib test. -
Install a Thermal Expansion Tank (If Needed)
Backflow preventer on the main line? Closed system. Heated water expands with nowhere to go -- pressure spikes. Expansion tank (2-5 gallon, rubber bladder) on the cold line near the heater absorbs it. Pre-charge set to match PRV outlet pressure (50-60 PSI). Without this, even a new PRV will not prevent thermal expansion spikes.
Tip: Check expansion tank pre-charge annually with a tire gauge on the Schrader valve. Bladder loses air over time. Recharge with a bicycle pump to match system pressure. -
Verify the Fix and Check for Damage
Test pressure at multiple locations: 50-60 PSI range. Then inspect for damage from the high-pressure period. Under sinks for supply line leaks, toilet fill valves for running, water heater T&P for discharge, washing machine hoses for bulging. Stressed components may need replacement even after pressure is corrected.
Tip: T&P valve was discharging? May need replacement even after pressure correction. Once it has discharged, the seal may not reseat properly. -
Establish Ongoing Pressure Monitoring
Test annually going forward. Permanent gauge on the main line or keep one in the toolbox. Document the reading each time. Creeping above 60? Adjust or plan replacement before it gets serious. Consistent monitoring catches deterioration early.
Tip: Smart water monitors alert you to pressure changes. Useful for vacation homes or properties not occupied full-time.
When to Call a Pro
Call a plumber for PRV replacement (main line work, meter shutoff required), if pressure is above 100 PSI (same-day urgent), if the T&P is discharging continuously, if you need an expansion tank, or if multiple fixtures are leaking from the high-pressure period. Plumber can also determine if your system is closed and size the tank.
Prevention Tips
- Test pressure annually. 30 seconds with a gauge catches deterioration before it causes damage.
- Replace PRV every 7-12 years proactively. Internal degradation is not visible from outside.
- Backflow preventer? Make sure an expansion tank is on the heater cold line. Without it, thermal expansion spikes regardless of PRV condition.
- Expansion tank pre-charge annually. Waterlogged tank (failed bladder) provides zero protection.
- Do not set above 60 PSI without a specific reason. Higher pressure accelerates wear on everything.
- Signs of high pressure (aggressive flow, hammer, running toilets, frequent leaks)? Test immediately, do not wait for the annual check.