Guide
Carbon monoxide and your boiler
How a boiler can produce carbon monoxide, warning signs, and what to do if an alarm goes off.
This is a referral line. When you call, you are connected with an independent local heating company.
Why it matters
The EPA describes carbon monoxide as odorless, colorless and toxic, and says it can kill before you are aware it is in your home. Sources include worn or poorly maintained boilers and furnaces, and flues that are blocked, leaking, disconnected or the wrong size.[source]
Alarms
Install carbon monoxide alarms and test them. NFPA publishes guidance on where to place them and how to maintain them.[source]
If the alarm sounds
Get everyone out into fresh air, then call 911 from outside. Do not go back in until responders say it is safe. Then have the boiler and venting checked before using it again.
Prevention
A yearly boiler service that checks combustion and venting, keeping vents clear of snow, and never running generators or grills indoors. Ready.gov repeats that last point for winter storms.[source]
About this guide. Written by Call Now Plumbing, a referral line operated by Get Called LLC, from the public sources listed on our sources page, checked Nov 3, 2026. It has not been reviewed by a licensed heating contractor. For advice on your system, ask the company you reach.
How a boiler makes carbon monoxide
Carbon monoxide forms when fuel burns without enough oxygen. A well tuned boiler venting properly produces very little and sends it outside. Problems start when the burner is dirty or out of adjustment, when the vent or chimney is blocked or disconnected, or when the heat exchanger is cracked. The EPA lists unvented or malfunctioning fuel burning appliances among the main indoor sources.[source]
Old chimneys are a particular risk around Utica, where so much housing is old.[source] A chimney that once vented a large boiler and water heater may not draft properly for a smaller modern appliance, and an unlined masonry chimney can deteriorate from the inside.
Symptoms to take seriously
CO poisoning symptoms are often described as flu like: headache, dizziness, weakness, nausea, confusion and shortness of breath. If several people in a house feel ill at the same time, or symptoms improve when you leave the house, treat it as a possible CO problem. Pets can be affected too.[source]
If you suspect CO, get everyone outside to fresh air and call 911. Do not wait for an alarm to confirm it.[source]
Alarms: where and how many
The NFPA recommends CO alarms outside each sleeping area, on every level of the home, and in other locations required by codes.[source] Test alarms monthly and replace them according to the manufacturer's instructions. Many CO alarms have an end of life signal after several years.
Combination smoke and CO alarms are fine as long as they are placed where both are needed. Do not put a CO alarm right next to the boiler, where brief readings on startup can cause nuisance alarms; follow the alarm's placement instructions.
Winter habits that cause CO poisoning
Winter outages and no heat emergencies are when CO cases rise. Never use a gas range or oven to heat the house. Never run a generator, grill or camp stove indoors, in a basement or in an attached garage, even with a door open.[source][source]
After a snowstorm, check that side wall boiler vents and furnace or water heater vents are clear. Snow drifting over a high efficiency boiler's vent can push exhaust back toward the house or shut the boiler down. Also clear the dryer vent.
What a heating technician checks
During a service visit, ask the technician to measure carbon monoxide in the flue gases and in the room, inspect the heat exchanger, check the venting connections and the chimney draft, and confirm the burner is adjusted correctly. Ask for the readings. A written combustion test is a reasonable request.
If your boiler has not been serviced in more than a year, schedule it before the cold weather. See the maintenance checklist.
After a CO alarm
Once responders say the house is safe, do not restart the boiler until a heating technician has inspected it, found the cause and fixed it. Ask what caused the alarm: a blocked vent, a cracked heat exchanger, a poorly adjusted burner, or something else. Keep the written findings.
Frequently asked
Does a CO alarm replace a smoke alarm? No. You need both, or combination units placed where each is needed.[source]My boiler is electric. Do I need a CO alarm? An electric boiler does not burn fuel, but a gas water heater, gas stove, fireplace or attached garage can still produce CO. Most homes with any fuel burning appliance or an attached garage should have CO alarms.The alarm chirps once a minute. That is usually a low battery or end of life signal, not an alarm. Check the manual. A continuous loud pattern is an alarm; get out.Can a chimney cause CO problems? Yes. A blocked, damaged or unlined chimney can let exhaust back into the house. Old masonry chimneys are common in older Utica area homes.[source] Ask your heating technician to check draft during service, and have the chimney inspected if there is any doubt.What reading is dangerous? Alarms are designed to sound before levels become dangerous for most healthy adults. Do not try to interpret a reading; if the alarm sounds, leave and call 911.Snow and vents after storms
Lake effect and nor'easter snow can bury side wall vents overnight. Make clearing the boiler and water heater vents part of your routine after shoveling the walk. Keep at least a foot of clear space around intake and exhaust terminations, and more if the manufacturer's instructions say so. The National Weather Service Binghamton office posts forecasts for the Utica area.[source]
Signs around the boiler
Soot around the burner door or vent connector, rust or water streaks on the vent pipe, a yellow or flickering flame on a gas burner where it should be blue, and a smell of exhaust are all reasons to have the boiler checked. These signs do not prove a CO problem, but they point to combustion or venting issues that can cause one.
Talk with your household
Make sure everyone in the house knows what the CO alarm sounds like and that the plan is to get out and call 911. Practice with children. Agree on a meeting spot outside, and keep phones charged in winter so someone can call from outside or a neighbor's house.
Space heaters and generators
Never run a generator, grill or camp heater indoors or in a garage during an outage. Keep generators well away from windows and doors.[source]
Common questions
Can a boiler give off carbon monoxide without smell?
Yes. Carbon monoxide has no smell, which is why alarms matter.[source]
Want a pro to look at it?
Call and get connected with a local heating company.
Call about your boiler(888) 835-0429