Is Your Boiler Safe? The Modern Carbon Monoxide Risk Checklist You Need in 2025 (UK Guide)
Quick Answer:
A boiler is not safe if you notice yellow flames instead of blue, black stains or soot, pilot lights cutting out, unusual condensation, or if a carbon monoxide alarm sounds. If this happens, **stop using it, open windows, leave your home, and call the National Gas Emergency Service on 0800 111 999 right away. To stay safe, have your boiler serviced every year by a Gas Safe engineer and fit EN 50291-approved CO alarms in the right places as per 2025 UK rules .
Table of Contents
What are the warning signs my boiler may be leaking carbon monoxide?
Where should I put a carbon monoxide alarm near a boiler in 2025?
What are the latest CO alarm rules for landlords in England?
What are the benefits of replacing an older boiler for safety?
What is carbon monoxide and why does it come from boilers?
Carbon monoxide (CO) is a deadly gas with no colour, smell, or taste. Boilers can give off CO when fuel isn’t burned completely – often due to poor servicing, blocked flues, or hidden faults. According to the Health and Safety Executive (HSE), CO can build up quickly and become fatal without warning .
What are the warning signs my boiler may be leaking carbon monoxide?
Here are 10 red flags that your boiler might be unsafe:
Yellow or orange flame instead of a steady blue one.
Black stains or soot marks around the boiler or flue.
Pilot light keeps blowing out.
Condensation on nearby windows.
Odd smells like burning or stale air.
Uneven heating or unexplained cold rooms.
Rumbling or kettling noises.
Frequent breakdowns or expensive repairs.
Energy bills creeping up with no change in use.
CO alarm going off.
The Gas Safe Register warns that even one of these signs is reason enough to book a professional check immediately .
What are the common symptoms of carbon monoxide poisoning?
Carbon monoxide poisoning can feel like the flu – but without a fever. According to the NHS, symptoms include:
Persistent headaches
Feeling lightheaded or dizzy
Nausea or sickness
Chest pain or shortness of breath
Confusion or drowsiness
Feeling better when you leave the house
If you or your family have these symptoms indoors, treat it as an emergency and call 999 .
How to act fast if I think my boiler is unsafe?
Follow this 6-step plan right away (per HSE guidance):
Turn off the boiler and stop using it.
Open windows and doors for fresh air.
Leave the property.
Call 0800 111 999 – the National Gas Emergency Service.
Get medical help (NHS 111 or 999 in severe cases).
Wait for a Gas Safe engineer to confirm the property is safe .
Where should I put a carbon monoxide alarm near a boiler in 2025?
According to BS EN 50292:2023 standards and the London Fire Brigade:
Place alarms 1–3 metres from your boiler.
On the ceiling at least 30 cm away from lights or walls, OR
On a wall 15–30 cm below the ceiling.
Fit alarms in every room with a combustion appliance and in bedrooms.
Avoid cupboards, bathrooms, or near vents.
Always choose alarms with the EN 50291 standard and a Kitemark symbol .
How often should I get my boiler serviced in the UK?
Homeowners: every year (strongly advised).
Landlords: legally required to service boilers annually and provide a Gas Safety Certificate.
The Energy Saving Trust also recommends regular servicing to keep boilers efficient and reduce the risk of CO leaks .
👉 Book your boiler service with Domestic Heating to stay safe and compliant.
What are the latest CO alarm rules for landlords in England?
Since October 2022, the UK Government requires:
Landlords to install CO alarms in all rooms with a gas or solid-fuel appliance.
Alarms to be kept in working order.
Failure to comply can mean fines of up to £5,000 .
What are the benefits of replacing an older boiler for safety?
Upgrading an older boiler means:
Lower risk of CO leaks.
Cheaper bills from higher efficiency.
Fewer breakdowns.
Quieter running.
Consistent heating.
Longer warranty cover.
Ready for hydrogen blends.
Greener heating with less CO₂.
Adds value when selling or renting.
Peace of mind knowing your family is safe.
What new trends in 2025 will help keep boilers safer?
Hydrogen-ready boilers preparing for cleaner fuel.
Smart CO alarms with mobile alerts.
AI-powered diagnostics for predictive servicing.
Hybrid systems combining boilers and heat pumps.
Government grants such as the Boiler Upgrade Scheme (£7,500 for heat pumps) to encourage safer, greener heating options .
FAQs on boiler safety and carbon monoxide
Do CO alarms expire?
Yes – usually after 5–7 years. Always check the expiry date.
Should alarms go high or low?
CO mixes with air, so both work. Just follow the 2025 placement rules above.
Can I use a combined smoke and CO alarm?
Yes, but only if it’s EN 50291-approved.
What number should I call in a CO emergency?
Always call 0800 111 999 (National Gas Emergency Service) .
Is servicing my boiler a legal requirement?
Not for homeowners, but it is strongly advised. For landlords, it’s the law .
Final thoughts
Boiler safety isn’t something to put off. Carbon monoxide is invisible but dangerous, and spotting the signs early can save lives. Check your boiler, fit alarms, book yearly servicing, and know what to do in an emergency.
👉 Live in Hertfordshire? Contact Domestic Heating for trusted boiler servicing and replacement.
