Quick Answer:

If you see pressure dips without pattern — short, irregular drops in water pressure that come and go — the backflow preventer or its internal checks are often the cause. Start by noting when the dips happen, then follow a few simple checks to confirm whether the backflow device is involved or if it’s something else on the supply line.

Why This Happens

• Backflow devices contain springs, seats, and check valves that control flow. Dirt, mineral buildup, or a worn seat can cause a valve to stick or flutter under changing flow, producing intermittent pressure loss.
• Thermal expansion, pump cycling, or changes in municipal supply pressure can interact with the backflow device and make drops unpredictable.
• Partial obstructions or a misaligned internal spring can open and close slightly during different flow rates, causing momentary dips rather than a steady low pressure.

Step-by-Step What to Do

1. Watch and record when it happens

Note times of day, which fixtures are running, and whether outdoor irrigation or appliances are on. This simple log helps separate patterns from random events.

2. Monitor the pressure gauge during flow cycles

Attach or observe the system pressure gauge while running a faucet or toilet flush. Monitor pressure gauge during flow cycles and watch for sudden drops or bouncing. If you see the needle dip when flow starts or during variable flow, the backflow device is a likely suspect.

3. Isolate sections of the plumbing

• Turn off irrigation, washing machine, and other nonessential supplies. See if the dips stop.
• Open a single faucet and observe the gauge; then open a second faucet and compare the behavior.

4. Inspect the backflow device visually

Look for obvious leaks, loose fittings, or corrosion. Do not disassemble the unit unless you are sure you know how — many backflow assemblies require certified testing after work.

5. Clean accessible strainers and aerators

Sometimes mineral flakes or debris downstream cause unstable flow. Clean faucet aerators and pre-filters, then re-check the pressure behavior.

6. Test under different flows

Try a steady moderate flow (one full faucet) and a higher flow (two or more fixtures). Note whether the dips correspond to low, medium, or high demand.

7. Consider temporary bypass or test port checks

If your installation has a test port or approved bypass, use it to check whether pressure stabilizes when the backflow device is isolated. Only perform this if the bypass is allowed by local code and you understand the risks of bypassing backflow protection.

What Not to Do

• Do not replace PRV prematurely. A pressure-reducing valve is often blamed, but replacing it before confirming the true cause wastes money and may not fix the intermittent dips.
• Do not force the backflow device open or remove parts without knowing local code requirements. Many assemblies must be tested and certified after any work.
• Do not ignore documentation or warning tags on the device — they often list required procedures and testing schedules.

When to Call a Professional

• If pressure dips continue after basic checks and gauge monitoring, call a licensed plumber experienced with backflow assemblies.
• Call a pro if the backflow device shows leaks, heavy corrosion, or if you suspect internal damage. Certified technicians have the parts and tests needed to repair or replace the assembly to code.
• If local regulations require testing or a certified repair, stop and call the appropriate professional rather than attempting an uncertified fix.

Safety Notes

• Never bypass a backflow device unless local code permits it and you follow approved procedures. Bypassing risks contaminating the potable water supply.
• Turn off supply and relieve pressure before touching fittings. Use basic protective gloves and eye protection when inspecting or handling plumbing parts.
• If you see signs of contamination or sewage backflow, evacuate affected plumbing sections and call a professional immediately.

Common Homeowner Questions

• Why does it only happen sometimes?
  Short answer: Small debris, a sticking seat, or pressure swings can make the valve act up only under certain flow conditions.
• Is this the same as low steady pressure?
  Short answer: No — intermittent dips are different from steady low pressure and usually point to a valve that is opening and closing improperly.
• Could I have this and also other issues?
  Short answer: Yes. Check for related problems like **low pressure after backflow** or **water hammer after backflow** that can coexist and help narrow the cause.