Quick Answer:
If a smart shutoff tripped and you now notice a sewer-like odor, it often means a trap seal was emptied or a fitting leaked when the device closed or drained part of the system. Start by inspecting the shutoff device and nearby valves, reset the device and slowly reopen valves while watching traps refill, smell-test floor drains and device fittings, confirm any auto-drain or primer features didn’t empty traps, and review the shutoff event logs to match timing. If you’re unsure or the smell persists, call a professional.
Why This Happens
Smart shutoff devices can protect your home from major leaks by closing valves or activating drains. That action can also temporarily remove the water barrier in traps (the curved pipes under sinks and floor drains) or activate an automatic drain feature. When a trap seal is lost, sewer gas travels up the drain and into the living space. Other causes tied to a shutoff event include:
- A closed main valve that routed water away from trap primers or allowed trapped water to drain.
- A leak at the device fittings or nearby joints that released sewer odors.
- An auto-drain or maintenance routine that emptied primer reservoirs.
- Timing: the odor often starts right after the trip, which is why checking event logs helps.
Step-by-Step What to Do
1. Inspect the shutoff device and nearby valves
Locate the device and any main or local shutoff valves it controls. Check whether the device closed a valve that could have allowed trap seals to drain (for example, valves on supply lines to trap primers or to fixtures with floor drains). Look for obvious water on or around fittings that might indicate a leak.
2. Reset the device and slowly reopen valves while checking traps
- Reset the smart shutoff according to the manufacturer’s directions so it won’t re-close while you work.
- Open any valves slowly and one at a time. Watch fixtures and floor drains for water returning into P-traps and for any immediate leaks.
- If traps remain dry, add water to each affected drain until the water level is visibly holding in the trap.
3. Do a targeted smell-test near floor drains and device fittings
- Move around the room with the odor and sniff near floor drains, sink drains, toilet bases, and the shutoff device fittings.
- Smelling strongest near a specific drain or the device fitting points to either a dry trap or a leak at that location.
4. Confirm any auto-drain features didn’t empty trap primers
Many smart systems or connected valves include automatic drain or maintenance modes. Check whether those features were active and if primer reservoirs or lines were emptied. If primer systems were drained, follow the manufacturer’s guidance to re-prime traps or refill reservoirs so trap seals are restored.
5. Review the shutoff event logs and correlate timing
Open the device or system app and review the event history. Note the exact time the shutoff tripped and compare it to when the smell started. A match strongly suggests the device action caused the odor and helps a technician diagnose which valve, drain or auto-drain routine is responsible.
What Not to Do
- Do not bypass safety devices to “clear” the smell. Bypassing or disabling a shutoff can allow uncontrolled water flow, causing flooding and hidden damage.
- Do not force-open valves or make jury-rigged connections under pressure—this risks injury and leaks.
- Do not ignore persistent odors; they can indicate a plumbing fault that will worsen over time.
- If the odor follows an automatic shutoff event or you suspect a device drained trap seals, call a pro rather than trying complex work-arounds yourself.
When to Call a Professional
Call a licensed plumber if any of the following apply:
- You can’t find the source or the smell returns after you refill traps.
- Multiple drains are dry or you suspect the device emptied primer systems.
- There is visible leaking at device fittings, or the device won’t reset or log events correctly.
- You’re uncomfortable resetting the device or working on valves tied into the protection system.
For related situations after work on pipes or fixtures, see Smell after plumbing repair for guidance on smells that follow manual repairs.
Safety Notes
- Ventilate the area—open windows and run exhaust fans to reduce odors quickly.
- Avoid prolonged inhalation of sewer gas. If anyone feels dizzy, nauseous, or unwell, get fresh air and seek medical help.
- Turn off electrical equipment near standing water and avoid working barefoot or with bare hands in contaminated water.
- Follow the device manufacturer’s reset and safety instructions exactly. If instructions are missing or confusing, stop and call a professional.
Common Homeowner Questions
- Could the shutoff alone cause the smell? Yes—if it closed or drained lines that let traps dry or emptied primer reservoirs.
- Will pouring water down the drains fix it? Often adding water to dry traps eliminates the smell, but if an auto-drain or leak is present the odor may return.
- Is sewer smell dangerous? Short exposure is usually unpleasant and irritating; prolonged exposure can cause symptoms—ventilate and call a pro if the source isn’t obvious or the smell persists.
More in this topic
For more related fixes and similar symptoms, see Sewer Gas Smell from Floor Drains.