Quick Answer:
If you notice a sewer-like smell right after changing a pressure regulator, don’t panic. Sudden pressure shifts can siphon water from fixture traps, allow brief reverse flow in the roof vent, or expose a failing backflow/check valve. Start by recording pressure readings, listening for gurgling at drains, and running fixtures to stabilize the system. If the odor persists or you see continuous gurgling, get a professional involved.
Why This Happens
When you change water pressure quickly, the plumbing system experiences a transient — a fast change in flow or pressure. That transient can do a few things that produce odors:
- Trap siphonage: a sudden drop can pull water out of sink, tub, or floor drain traps so sewer gas reaches the home.
- Reverse vent flow: a pressure swing can push or pull air briefly through the roof vent instead of up and out.
- Backflow/check valve issues: a failing device can leak or open during a transient, letting contaminated water or air move the wrong way.
If the pattern includes times or conditions like Odor only at night, note that—timing helps point to traps, vents, or appliance cycling as the cause.
Step-by-Step What to Do
Step 1 — Record before-and-after pressure readings
- Before you adjust a regulator again, note the pressure reading on the gauge. Typical home pressure is often 40–60 psi, but check your local norm.
- After an adjustment, write down the new reading and the time. These records show whether the regulator is holding steady or bouncing back.
Step 2 — Check for gurgling or sputtering at fixtures
- Run hot and cold taps, flush toilets, and run a shower. Listen at nearby drains for gurgling, sputtering, or bubbling—signs that a trap has been partially siphoned.
- Test uncommon drains (garage, basement floor drains) as they often lose water in the trap first.
Step 3 — Inspect the backflow preventer and check valves
- Look at visible backflow devices and check valves for drips, wet stains, or corrosion. A leaking connection can let sewer gas or contaminated water bypass protections during a pressure swing.
- If the device has test ports, note whether water appears at the cover after a transient. Don’t disassemble sealed or certified backflow devices unless you are qualified.
Step 4 — Run multiple fixtures to normalize pressure and observe the odor
- Open several faucets at once (kitchen, laundry, outdoor hose bib) to allow pressure and flow to settle across the system. This often stops short-lived siphon events.
- Watch whether the odor fades as pressure evens out. If it does, the issue was likely a transient rather than permanent equipment failure.
Step 5 — Look at the roof vent for brief reverse flow during transients
- If safe, have someone watch the roof vent while you create a controlled pressure change (run multiple fixtures) to see whether air is pushed out or briefly drawn back in.
- Do not climb on the roof alone or in unsafe conditions. If you can’t observe safely, skip this and call a pro.
What Not to Do
- Avoid resetting regulators repeatedly without diagnosing the cause—this can mask trap-siphon events and make the real failure harder to find.
- Do not ignore continuous gurgling or persistent sewer smell; those are signs of a sustained problem.
- Call a professional when odors follow pressure adjustments or you notice continuous gurgling at drains.
When to Call a Professional
- If the odor does not go away after running fixtures and stabilizing pressure.
- If you find a leaking backflow preventer, a non-sealing check valve, or repeated trap siphonage.
- If you see continuous gurgling from drains, sewage backup, or any unsafe plumbing condition.
Safety Notes
- Do not climb on the roof alone or in bad weather. Observe vents from a ladder or let a pro inspect them.
- Don’t open sealed backflow devices or tamper with their test ports unless you are certified to do so—improper handling can make cross-connection hazards worse.
- If you smell gas (natural gas), leave the house and call your gas company or emergency services. Sewer-like odors are unpleasant but different; always err on the side of caution.
Common Homeowner Questions
- Why did changing a regulator cause smell now?
A sudden adjustment can create pressure transients that siphon traps or force air through vents and weak valves. - Will running faucets fix it?
Often yes for short-lived transients—running multiple fixtures can re-fill traps and normalize pressure. - Can I test the backflow device myself?
You can visually inspect for leaks, but functional testing and repairs should be done by a qualified plumber or certified tester.
More in this topic
For more related fixes and similar symptoms, see Sewer Gas Smell from Floor Drains.