Water Pressure Over 80 PSI:
Pressure Regulators, Expansion Tanks and What High Pressure Does
Strong pressure feels great in the shower. Above 80 psi, it’s working on every hose, valve and fitting in the house, every hour of the day.
Russ screws a pressure gauge onto a hose bib on every inspection. In his recent reports, 42 houses read above 80 psi. One Vancouver house measured 120 psi. A Springfield house hit 150 at the front hose bib and 110 at the back, and the front spigot was leaking. A few houses sat at the other end, around 40 psi.
High pressure doesn’t feel like a problem. It shows up later as leaks.
Real Inspection Photos
Water Pressure Readings From Russ's Inspections
Gauge readings at hose bibs from Russ's recent reports.
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This hose bib read 150 psi, nearly twice the 80 psi limit. -
A reading above 80 psi at an exterior hose bib. -
Water pressure above 80 psi measured at the hose bib. -
Another reading above 80 psi. -
About 40 psi, the low end of typical.
What 80 psi means
Plumbing codes used in Oregon and Washington cap the static water pressure inside a house at 80 psi. Above that, they call for a pressure-reducing valve (PRV) to bring it down. Many plumbers prefer something closer to 50 to 70.
Russ’s report wording: water pressure above 80 psi can place undue stress on plumbing fixtures, appliances and pipes. Every washer hose, toilet fill valve, dishwasher valve, faucet cartridge and supply line is rated for a pressure range. Run them above it for years and they wear out faster. The supply lines post covers the small hoses that usually fail first.
Where high pressure comes from
Water providers set street pressure for their whole system. Houses low on a hill, or near a pump station, can get far more than they need. In those neighborhoods, a PRV is standard.
Most PRVs sit where the main line comes into the house: in the basement, the crawlspace, the garage or a box near the meter. They’re bell-shaped brass valves with an adjusting screw on top. Like any valve, they wear out. When one fails, pressure creeps up toward street pressure, often without anyone noticing.
The main shutoff is usually close by. The post on the main water shutoff and the meter box covers where to look.
A house reading well over 80 either has no PRV or has one that isn’t doing its job. A licensed plumber can tell which and set or replace it.
Thermal expansion and the expansion tank
A PRV has a side effect. It works like a one-way valve, so water in the house can’t push back into the street. When the water heater heats a tank full of cold water, the water expands, and in a closed system that expansion raises the pressure in every pipe.
A thermal expansion tank on the cold line at the water heater gives that expansion somewhere to go. Many jurisdictions require one when the system is closed. Without it, pressure spikes after every heating cycle, and the water heater’s relief valve is often the first thing to drip. The relief valve discharge pipe post covers what that valve should look like.
Low pressure and poor flow
Low pressure came up less often. In Sandy and Vancouver, Russ measured about 40 psi at an exterior spigot, which his reports noted meets typical minimums but can make for weak showers when two fixtures run. A Portland house measured about 45.
Low flow at one fixture is different from low pressure everywhere. A clogged aerator, a partly closed valve or old galvanized pipe can choke a single faucet. In one Portland house, flow at a fixture was poor, and in a Vancouver house, the kitchen faucet dropped noticeably while the dishwasher filled. Those get a plumber’s look, especially in older homes.
What Russ checks
He measures static water pressure with a gauge at a hose bib or laundry connection, runs multiple fixtures to check flow, and looks for a PRV and an expansion tank where they’re visible. He looks for leaks and signs of past leaks around fixtures, valves and the water heater. He doesn’t adjust or test PRVs. Pressure over 80 psi gets a recommendation for a licensed plumber to evaluate and correct it.
- Screw a gauge onto a hose bib with everything else off and read it
- Look near the main shutoff for a bell-shaped brass PRV
- Look for a small tank on the cold line at the water heater
- Check the water heater relief valve pipe for drips or a bucket
- Run the shower and a sink at once and watch the flow
House water pressure should stay at or below 80 psi. In Russ’s reports, 42 houses measured above that, some well above. A plumber can install or adjust a pressure-reducing valve, and an expansion tank usually goes with it.
For the rest of the plumbing, the guide to what to look at in the plumbing before you make an offer covers pipe materials, drains and the water heater. To set up an inspection, you can book online.
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