Open and closed systems
In an open system, water warmed in the heater can push back toward the street supply, so pressure stays steady. Many homes are now closed systems, because a pressure regulator, backflow device or check valve at the meter or main stops water from flowing backward. When the heater fires, the expanding water has nowhere to go, and house pressure climbs.
Those repeated pressure spikes stress the tank, the relief valve, toilet fill valves, faucet cartridges and appliance hoses. A common symptom is a relief valve that drips during or after a heating cycle. A thermal expansion tank, a small tank with an air cushion behind a rubber diaphragm, gives that expanding water somewhere to go.
Signs of a pressure problem
How a plumber checks pressure
- Static pressure test.A gauge on a hose bib or the heater drain shows house pressure with no water running.
- Watch over a heating cycle.A gauge that records the peak shows whether pressure jumps when the heater runs.
- Check the regulator.If pressure is high even when cold, the pressure regulator may be failing or set too high.
- Check the expansion tank.An existing tank can lose its air charge or have a ruptured diaphragm. Tapping it or checking the air valve tells the plumber a lot.
- Recommend the fix.Adjust or replace the regulator, add or replace the expansion tank, or both.
Matching the fix to the finding
| What the gauge shows | Likely cause | Typical fix |
|---|---|---|
| High pressure all the time | Missing or failed pressure regulator | Install or replace the regulator |
| Normal when cold, spikes when heating | Closed system without working expansion control | Add or replace an expansion tank |
| Spikes even with an expansion tank | Tank waterlogged or air charge lost | Recharge or replace the expansion tank |
| Normal pressure, valve still drips | Worn relief valve or overheating | Check thermostat, then replace the valve |
Questions to ask
- What is my house water pressure, static and during heating?
- Is my system closed, and what makes it closed?
- Does my pressure regulator need adjusting or replacing?
- If you add an expansion tank, how will it be supported and charged?
Common questions
Does every water heater need an expansion tank?
Not every one. It depends on whether the plumbing is a closed system and what local code requires. A plumber can check, and the City of Brea can confirm current requirements.
How do I know my expansion tank has failed?
A failed tank often feels full of water all the way up when tapped, or water comes out of its air valve. Relief valve drips may also return.
Can high water pressure damage my water heater?
Repeated high pressure and spikes add stress to the tank and fittings, and can make the relief valve open often. Keeping pressure in a normal range helps everything in the system last.
General information for Brea, not a quote or professional advice. In an emergency, call 911.