Carbon Monoxide Alarm Going Off or Beeping: What to Do

Alarm or chirp: how to tell which one you have

Carbon monoxide alarms make two very different noises, and the difference matters. The alarm itself is loud, piercing and repeated, usually a burst of beeps, a pause, then another burst, carrying on until the air clears or someone deals with it. Many models also flash a red light at the same time.

A chirp is a single short beep, or a small group of beeps, repeated every 30 to 60 seconds or so. It is the alarm asking for attention: low battery, a fault, or the sensor reaching the end of its working life. The exact pattern varies between makes, and it is printed on the back of the alarm or in the leaflet that came with it. If you cannot tell which you are hearing, treat it as an alarm until you have checked.

• Loud, repeated, often with a flashing red light: carbon monoxide detected. Act now.
• A single chirp at regular intervals: usually a low battery.
• A different chirp pattern, sometimes with a yellow or amber light: often end of life or a fault. Check the label.
• Beeping three times, or another fixed number of times: on some models this is a specific fault or end of life signal. The label on the back tells you which.

What to do when the alarm goes off

Pressing the test or silence button does not remove the gas. Taking the battery out does not either, and it leaves you with no warning if the level rises again. If the alarm stops once you have opened windows and turned things off, that does not mean the problem has gone. It means the air has cleared for now.

If you are not sure where the controls are, our guide on how to turn off a boiler shows the power switch, the fused spur and the gas lever at the meter. It is worth knowing before you ever need it.

• Open doors and windows to let fresh air in.
• Turn off the boiler, gas fire, cooker or any other fuel burning appliance if you can do it quickly and safely. Do not stay inside to do it.
• Get everyone out, including pets, into fresh air.
• Call the National Gas Emergency line on 0800 111 999. The line is free and open day and night, whoever supplies your gas. If you use oil or solid fuel, call a qualified engineer for that appliance.
• If anyone has symptoms, get medical advice. Call 999 if someone is confused, drowsy, has collapsed or has chest pain.
• Stay out until the emergency engineer has attended and told you it is safe to go back in.

Carbon monoxide has no smell, no colour and no taste. You cannot rule it out by sniffing the air. The alarm is the only reliable warning you have.

Symptoms to watch for

Low level carbon monoxide poisoning is easily mistaken for a cold, flu or tiredness. The signs are headaches, dizziness, feeling sick, tiredness, breathlessness and confusion. The clue is the pattern: symptoms that ease when you are out of the house and come back when you return, several people or pets in the home affected at once, or symptoms that are worse in the room with the boiler or fire.

If you recognise that pattern, even without an alarm, get out into fresh air, call 0800 111 999 and get medical advice. Tell the doctor you think carbon monoxide may be involved, because it is not always the first thing they will test for.

What happens after you call

An emergency engineer from the gas network will come out, check the air and the appliances, and make the property safe. If they find an appliance producing carbon monoxide, they will turn it off and label it as unsafe. It must not be used again until a Gas Safe registered engineer has repaired it. Do not be tempted to turn it back on or reset it. Our guide on how to reset a boiler explains when a reset is appropriate, and this is not one of those times. The emergency service makes things safe; it does not fix the boiler or the fire.

That is often where people are left with no heating or no hot water. If the boiler has been capped off and you have a hot water cylinder, the immersion heater will usually still give you hot water while you wait for the repair. Our guide on how to get hot water without a boiler covers the other options.

Why alarms go off more once the heating comes back on

Autumn is when a lot of carbon monoxide alarms go off for the first time. A boiler or gas fire that has sat unused all summer is suddenly running for hours a day, often with windows closed and draughts sealed for the winter. Problems that were already there, a partly blocked flue, a bird or wasp nest in a chimney, a burner that needs cleaning, or a flue joint that has come apart inside a boxing, start to show. Our guide on when to turn the heating on lists the checks worth doing on the first cold day.

The usual causes an engineer looks for are:

• A boiler or gas fire that has not been serviced and is burning poorly.
• An older open flued appliance such as a gas multipoint water heater or a back boiler behind a fire, especially one that has been spilling fumes for a while.
• A blocked or damaged flue, or a chimney that needs sweeping on an open fire or wood burner.
• Not enough ventilation for an older open flued appliance, often after new windows or blocked air vents.
• Fumes from outside: a neighbour's flue close to an open window, a car running in an attached garage, or a barbecue or generator near the house.

Can a carbon monoxide alarm go off for no reason?

Genuine false alarms are less common than people hope. Some sensors can react to other gases, such as fumes from solvents, paints or strong cleaning products in a small closed room, and an alarm near its end of life can become unreliable. But the only safe way to find out is to have it checked. Calling 0800 111 999 costs nothing, and the emergency engineer will not think less of you for a call that turns out to be nothing.

If the alarm keeps going off on different days, do not just move it or replace it and hope. Have every fuel burning appliance in the home checked by a Gas Safe registered engineer. An alarm that goes off repeatedly with no obvious cause is one of the clearest reasons there is to book that check.

Dealing with a chirping alarm

If the chirp is a low battery and your alarm has a replaceable battery, change it and press the test button to check it sounds. Many modern alarms have a sealed battery designed to last the whole life of the alarm, typically seven to ten years. On those, a chirp means the whole unit needs replacing. The expiry or replace by date is usually printed on the side or back.

When you replace it, buy an alarm marked as meeting BS EN 50291, and fit it in the same room as the boiler or other fuel burning appliance. The maker's instructions give the exact position, but the usual guidance is one to three metres away from the appliance, either on the ceiling away from the walls or high on a wall above the height of any door or window. Keep it out of cupboards, away from extractor fans and not directly above a cooker or sink. A second alarm in the bedroom most used gives an extra layer of warning at night.

Getting the boiler checked

Once the emergency service has made things safe, the appliance that caused the alarm needs proper diagnosis and repair before it goes back into use. A boiler diagnosis visit works through the gas, flue and combustion side and ends with proof of what is wrong rather than a guess. Call us on 020 4652 5111 or send an enquiry, tell us what the emergency engineer found and what label they left on the appliance, and we will tell you what happens next. We have 20 engineers across London, and our rate is on the pricing page and agreed before we attend. Whoever works on a gas appliance must be on the Gas Safe Register, so ask to see their card, or check a plumber on the Gas Safe Register yourself before they arrive.

If you have also noticed a smell of gas rather than an alarm, the steps are different. Our guide on what to do if you smell gas goes through them in order.