Why is my carbon monoxide alarm beeping?

First, rule out a real alarm

Carbon monoxide has no colour, smell or taste. Gas Safe Register says that if your alarm is sounding continuously, CO could be in the air. Do not try to work out the beep pattern first. Act first:

1. Turn off the boiler, fire, cooker or other gas appliance, if it is safe to do so.
2. Open doors and windows to let fresh air in.
3. Get everyone out into fresh air, including pets.
4. Call 0800 111 999, the free National Gas Emergency Service.
5. Get medical advice. Gas Safe says to call NHS 111 if you suspect CO poisoning, and 999 or go to A&E if someone has severe symptoms such as difficulty breathing, sudden confusion or loss of consciousness.

Stay out until you are told it is safe. In north and east London, the emergency engineer comes from Cadent, which runs the local gas network. They will make the situation safe. A Gas Safe registered engineer then needs to find and fix the fault before the appliance is used again.

Signs it might be CO, not a fault

The NHS lists the main symptoms of carbon monoxide poisoning as a headache, dizziness, feeling or being sick, and feeling weak. Gas Safe adds some other clues:

• Symptoms that ease when you leave home
• Other people in the house feeling unwell at the same time
• Pets acting oddly

Gas Safe also lists signs on the appliance itself: a floppy yellow or orange flame, sooty marks, a pilot light that keeps going out, and more condensation on windows than usual. If you notice any of these alongside a beeping alarm, treat it as an emergency.

The usual non emergency reasons

Once you are sure there is no CO, the beeping usually has a simpler cause. Gas Safe says the reasons vary by model, from low battery to a device fault, and to check the manufacturer’s instructions. Patterns differ between makes, so the table below is a guide to what to look up, not a code list.

What you hear or see	Likely meaning	What to do
Loud, continuous or repeating alarm	CO detected	Follow the emergency steps above
Short chirp every minute or so	Often a low battery warning	Check the manual, then replace the battery or alarm
Chirps plus a fault light	Often a sensor or device fault	Replace the alarm
Regular chirps on an alarm five to ten years old	Often an end of life warning	Replace the whole alarm
A beep when you press the test button	Normal self test	Nothing, the alarm is working

Gas Safe says most CO alarms last five to ten years. Most have a date printed on the back. If yours is older than its stated life, replace it even if it is not beeping.

Why flats get more false worries

In blocks across Bethnal Green and Bow, and in purpose built flats generally, the boiler is often in a kitchen cupboard a metre from the cooker. Some alarms end up fitted right beside the cooker or in a steamy corner, and manufacturers usually give distances to keep from both. Gas cookers are excluded from the landlord CO alarm rules, but they still burn gas and produce some combustion products.

Placement matters. Follow the manufacturer’s fitting instructions. Our guide on where to put a carbon monoxide alarm goes through rooms with boilers, fires and bedrooms.

Never move an alarm to stop it going off. If it keeps alarming near a particular appliance, that appliance needs checking.

Choosing a replacement

Gas Safe Register recommends an audible alarm with a Kitemark to BS EN 50291-1:2010 for homes (BS EN 50291-2:2010 is for caravans and boats). It does not recommend “black spot” warning cards, because they make no sound and will not wake you.

Some points when buying:

• Sealed battery alarms with a long life save battery changes, but must be replaced as a unit at the end of their life.
• Mains alarms suit some installations and are often linked to smoke alarms.
• A standard smoke alarm does not detect CO. Gas Safe is clear on this.
• A CO alarm is not a gas leak detector unless the maker says it has that feature.

Renting: who replaces it?

In England, the 2022 regulations require landlords to fit a CO alarm in any room used as living accommodation that has a fixed combustion appliance, excluding gas cookers. The GOV.UK guidance says landlords must repair or replace alarms once they are told they are faulty. If you rent and your alarm is chirping, tell your landlord or agent in writing.

Having the appliances checked

A beeping alarm is a good moment to book a check of the boiler and any gas fire. An annual service and safety check is the best way to stop CO being produced in the first place. Gas Safe calls the alarm a second line of defence, not a replacement for maintenance. See our carbon monoxide alarms and gas safety check pages to book.