· Michael Blair
Almost nobody calls a plumber about high water pressure, which is why it does so much damage. Municipal mains have to deliver enough pressure to serve the highest and furthest property on the line, and homes closer to the source get whatever that requires. Fixtures are rated for far less.
What the numbers should be
Residential fixtures are generally designed around 40 to 60 psi. Most plumbing codes cap incoming pressure at 80 psi, and above that a pressure-reducing valve is required rather than optional. Mains pressure in parts of Middle Tennessee comfortably exceeds that figure.
A gauge that screws onto a hose bib costs very little and answers the question in a minute. Test with everything in the house off, and test in the evening as well as the morning, because municipal pressure varies with demand across the day.
What it damages first
Appliance inlet valves. Washing machine and dishwasher solenoids are the most common early casualty, and they tend to fail in the position that lets water keep coming. Supply hoses are next, particularly the rubber ones.
After that: toilet fill valves that never quite shut, taps that drip within a year of being reseated, and the water heater’s temperature and pressure relief valve weeping because the system has nowhere to expand.
Thermal expansion, and why a PRV needs a tank
A pressure-reducing valve is usually a one-way device. Once it is fitted, the house becomes a closed system, and heated water that expands can no longer push back into the main. Pressure climbs every time the heater fires.
That is what a thermal expansion tank is for. Fitting a PRV without one moves the problem rather than solving it, and the symptom is a relief valve that discharges periodically for no obvious reason. If a plumber quotes a PRV with no expansion tank, ask why.
Whether yours is working
PRVs are wear items. They typically last somewhere between ten and fifteen years, and they fail gradually rather than suddenly, drifting upward until the house is back on mains pressure without anything obviously changing.
If your house has one, testing pressure annually is a two-minute job that catches the drift. A reading that has climbed since last year means the valve is on its way out, and replacing it is far cheaper than the appliances it protects.