Carbon monoxide alarms after an ECO4 boiler change: what UK households should check (2026)

Guide by ApplyFreeBoiler.uk (Reliant Energy Solutions Ltd), a heating and insulation installer in Bury, Greater Manchester. We are not the government, Ofgem or an energy supplier.

A new boiler changes the heating appliance in the home, so it is worth checking what carbon monoxide alarm is in place afterwards. This page is general household information about alarms, testing and what to do if one sounds; it is not a legal opinion and does not guarantee funding. ApplyFreeBoiler.uk is a heating and insulation installer in Bury, not the government, Ofgem or an energy supplier.

1. Ask the installer what they fitted or left in place

Before the team leaves, ask whether a carbon monoxide alarm was supplied, moved or left as it was, and where it is. Write down the make if it is printed on the unit, and keep any leaflet that came with it. If no alarm was discussed, ask what they recommend you check in the home; this page does not claim that every job must include a new alarm.

2. Find the test button and try it as the maker describes

Most household alarms have a test button. With the instructions in front of you, press it and listen for the alert sound so you know what it should be like. If there is no sound, the unit looks damaged, or you cannot find instructions, ask the installer or the aftercare number rather than assuming it is working.

3. Check that it sits at a high level

Many carbon monoxide alarms are designed to be placed at a high level on a wall or ceiling, away from very damp or steamy spots, following the maker's leaflet. Do not hide the unit behind furniture, inside a cupboard or on a low shelf unless the instructions say that is correct for that model. If the alarm was moved during the boiler work, ask for it to be put back where the leaflet says it should go.

4. Note which rooms it covers

Look at whether the alarm is in the same room as the boiler or in a hallway nearby, and whether there is any other alarm elsewhere in the home. Ask the installer to explain what they have left and what, if anything, they suggest you add. Do not treat one alarm as covering every room unless the instructions say so.

5. Know what to do if the alarm sounds

If the alarm goes off, treat it as urgent. Leave the property, get into fresh air and call the National Gas Emergency Service on 0800 111 999, the published UK gas emergency number. Do not go back inside until you have been told it is safe. Ask a qualified engineer to check the appliance before you use it again. If anyone feels unwell, get medical help.

6. Look at the expiry or replace-by date

Many alarms have a replace-by date printed on the case or in the leaflet. Note that date in the same folder as your install paperwork. This checklist does not set a replacement interval; follow the date and the maker's instructions for that unit.

7. Keep a short written record

Write down where the alarm is, the date you last used the test button, and the aftercare number you were given after the boiler change. If the alarm later beeps in a short chirp rather than a full alert, check the leaflet: that can mean a low battery or an end-of-life warning, which is different from a full alarm.

8. Do not ignore later warning signs around the appliance

Stains, soot, a lazy or yellow flame where you would normally expect a clear burn, or household members feeling unwell when the heating is on, are reasons to stop using the appliance and get it checked by a qualified engineer. Those signs are not a diagnosis, and this page is not a substitute for emergency help or a professional inspection.

9. Compare local delivery data

See ECO measures by council on ApplyFreeBoiler.uk, built from DESNZ Household Energy Efficiency statistics, to see how many ECO measures have been installed in your local authority area.

10. Check eligibility

Use the ApplyFreeBoiler.uk eligibility check to see whether an ECO4 heating or insulation pathway may be available for your home in England, Scotland or Wales. ECO4 is due to close on 31 December 2026.