# Carbon monoxide safety around a boiler

Know the warning signs and keep alarms and maintenance separate.

Updated 2026-11-10. Also on the [web page](https://boilerpros.fyi/guides/carbon-monoxide-safety).

Carbon monoxide is a poisonous gas. HSE and CDC say you cannot see or smell it. A boiler that seems to run normally is not proof that combustion is safe. [HSE and CDC, checked 2026-11-10.]

## If an alarm sounds or exposure is suspected

Go outside to fresh air. Get urgent medical advice if anyone has symptoms or may have been exposed. Contact the local emergency service from a safe place. Do not stay inside to investigate, silence the alarm and carry on, or wait for a routine service appointment. Follow the emergency responder's instructions before returning.

HSE's carbon monoxide page advises urgent medical help for suspected poisoning. CDC explains that exposure can cause loss of consciousness or death. [HSE and CDC, checked 2026-11-10.]

## Symptoms can be unclear

CDC lists headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion among common symptoms. HSE notes that symptoms can resemble common illnesses. Symptoms alone cannot confirm or exclude exposure. Tell medical staff that carbon monoxide is suspected. [HSE and CDC, checked 2026-11-10.]

Do not use the absence of a smell as reassurance. Do not rely on an app, a directory tool or an internet checklist to decide whether a building is safe.

## Alarms and servicing

HSE recommends carbon monoxide alarms as a useful additional precaution. It says they are not a replacement for regular maintenance and safety checks. Install and maintain alarms according to their manufacturer's instructions. Ask the relevant local authority about rules for your property. This guide does not set alarm-placement law across different countries. [HSE homeowner guidance, checked 2026-11-10.]

CDC recommends yearly service of heating systems and other fuel-burning appliances by a qualified technician. Keep vents clear and ask a qualified person to investigate faults. Do not open the boiler casing or adjust combustion settings. [CDC, checked 2026-11-10.]

## After a suspected incident

Keep the appliance out of use until the appropriate professional says it can be used. Save the inspection findings and repair report. Ask what caused the problem and whether other equipment needs attention.

A service reminder helps organise maintenance. It cannot detect carbon monoxide or grant permission to use an appliance after an incident.

## Sources

All sources below were fetched on 2026-11-10. This is the date checked, not a claim about the publication date. Recheck current terms before booking.

- [HSE, Carbon monoxide poisoning](https://www.hse.gov.uk/gas/domestic/co.htm), checked 2026-11-10.
- [CDC, About carbon monoxide poisoning](https://www.cdc.gov/carbon-monoxide/about/index.html), checked 2026-11-10.
- [HSE, Gas safety for homeowners](https://www.hse.gov.uk/gas/domestic/faqownerocc.htm), checked 2026-11-10.

## Questions

### Can an alarm replace a boiler service?

No. HSE says alarms are an additional precaution and do not replace maintenance and safety checks.