How to fit a carbon monoxide alarm

Helpful video reference. FireAngel Safety Technology's fitting guide for their CO-9B carbon monoxide alarm covers the key steps: positioning, wall mounting, initial test and what the alarm sounds like in operation. FireAngel is a UK-based manufacturer with products certified to the relevant British and European standards. Watch on YouTube.

1. Understand when a CO alarm is legally required

Since October 2022 (The Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022), all private rented properties in England must have a carbon monoxide alarm in any room with a fixed combustion appliance such as a gas boiler, wood-burning stove or open fire. This also applies to any solid-fuel appliance.

Owner-occupiers are strongly recommended to follow the same rule. New builds must comply under Building Regulations Part J.

2. Choose the right type

• Battery sealed (10-year life): simplest, no wiring, suits most domestic installations.
• Battery replaceable: lower upfront cost but running expense and maintenance over time.
• Mains-powered interlinked: harder to silence or bypass, required on some specifications and by some landlords. The interlinked option connects to a mains supply and to other alarms in the home, so all sound together. This type needs an electrician to fit if new wiring is required.

Look for a BS EN 50291-1 mark (household use) or BS EN 50291-2 (vehicles and boats).

3. Find the right position

Place the alarm on the ceiling or wall in the same room as the combustion appliance, between 1 m and 3 m horizontally from it. CO disperses fairly evenly in air, so it does not pool at floor level the way LPG does. Fitting on the ceiling or at head height (around 1.5 m from the floor) is correct.

Do not fit it directly above a cooker, in a cupboard, behind a curtain, directly above or beside an air vent, or in a garage where vehicle exhaust could trigger it. The instruction leaflet supplied with the alarm will show a room diagram. Follow it.

4. Mount the alarm

Mark the two fixing holes with a pencil using the supplied backplate. Drill and plug the holes. Most domestic CO alarms only need a small No. 5 or No. 6 plug. Screw the backplate to the wall.

Fit the battery (twist or slide the cover off depending on the model), then click or twist the alarm body onto the backplate. For a ceiling-mounted disc alarm, the fixing method is the same but the alarm sits flush against the ceiling.

5. Test immediately

Press and hold the test button until the alarm sounds (usually 2 to 4 seconds). This tests the electronics and the sounder, but not the CO sensor itself. The electrochemical sensor cannot be triggered by the test button. Some manufacturers supply a test spray for sensor function checks, but most homeowners rely on the button test and trust the manufacturer's stated sensor life.

If the alarm does not sound, check the battery connection first.

6. Maintain and replace on schedule

Most modern CO alarms have a 7 to 10 year rated sensor life. The alarm will emit a regular single chirp or a fault code when the sensor approaches end of life. Record the installation date on the unit or in a home maintenance log. Do not try to repair or reuse an alarm past its expiry date.

When to call us

An electrician's role with CO alarms is fitting mains-powered interlinked systems where new wiring is needed, or where a landlord needs the work certified. Battery alarms are genuinely DIY-suitable. If you have a mains-connected alarm that has failed or is not triggering correctly, or if you want interlinked smoke, heat and CO alarms running from the same circuit, that is a job for Richard.