Carbon monoxide alarm going off near the water heater

Symptoms

• CO detector alarm sounds, especially one located near the water heater or its vent path
• Possible headache, dizziness, or nausea in household members
• Gas water heater has been running recently
• Vent or flue may look damaged, disconnected, or blocked

Likely causes

• CommonVent pipe disconnected, blocked, or corroded, allowing exhaust into the living spaceCombustion gases that should exit through the flue can leak into the home if the venting fails.
• CommonBackdrafting caused by exhaust fans or a depressurized house pulling flue gases back indoorsPowerful exhaust fans can sometimes overcome the natural draft of the water heater's flue.
• PossibleIncomplete combustion from a dirty burner or insufficient air supplyA poorly burning flame produces more carbon monoxide than a properly tuned one.
• PossibleBlocked or bird-nested vent termination outsideAn obstruction at the outside vent opening prevents exhaust from escaping.

What to do

1. Get everyone, including pets, out of the house immediately into fresh air.
2. Call 911 or your local emergency number and report a carbon monoxide alarm.
3. Do not go back inside until emergency responders say it's safe.
4. Turn off the gas water heater only if you can do so quickly and safely on your way out; do not delay evacuating to do this.
5. Once cleared as safe, do not use the water heater again until a licensed technician has inspected the venting, combustion air supply, and burner.
6. Have working carbon monoxide detectors installed on every level of the home and near sleeping areas going forward.

Tools and parts

• None; this is an evacuate-and-call situation

When to call a pro

A licensed plumber, HVAC technician, or your gas utility should inspect the venting and combustion system before the unit is used again.

Safety