During a recent routine boiler service, our engineers at Alliance CFM identified a carbon monoxide leak caused by a failed internal gasket. The issue was not visible externally and the boiler was still operating, but testing confirmed unsafe combustion gases escaping within the casing.
This type of fault highlights exactly why annual boiler servicing is essential.
What Causes a CO Leak in a Boiler?
A carbon monoxide leak from a boiler is most commonly caused by:
- A deteriorated combustion chamber gasket
- A failed heat exchanger seal
- Loose or incorrectly seated burner seals
- Corrosion around flue joints
- Cracked internal components
In this case, the gasket that seals the combustion chamber had degraded over time. When the seal fails, combustion gases can escape into areas of the appliance they should not. While modern boilers are room sealed, internal leakage can still present a serious safety risk and lead to incomplete combustion.
How Is a CO Leak Found During a Boiler Service?
A proper boiler service is far more than a visual check. When our Gas Safe engineers carry out servicing, we:
- Inspect and test all combustion seals and gaskets
- Remove and check the burner assembly
- Analyse flue gases using a calibrated flue gas analyser
- Check for signs of corrosion or heat damage
- Inspect the heat exchanger and combustion chamber
- Test the integrity of the flue system
In this instance, flue gas readings were outside expected parameters. Further inspection revealed the failed gasket, which was allowing combustion gases to escape internally.
Without a service, this fault could have gone unnoticed.
Signs Your Boiler May Have a Failed Gasket
A gasket failure does not always present obvious warning signs, but common indicators can include:
- Unusual combustion readings during servicing
- Sooting inside the case
- Burning smells
- Boiler lockouts
- Increased condensation inside the casing
If any of these symptoms are present, the boiler should be isolated and inspected by a qualified engineer immediately.
Is a Failed Boiler Gasket Dangerous?
Yes. A failed combustion gasket can lead to carbon monoxide production or leakage if left unresolved. Even if the appliance appears to be working normally, unsafe combustion can develop over time.
Carbon monoxide exposure can cause:
- Headaches
- Dizziness
- Nausea
- Fatigue
- In severe cases, unconsciousness
This is why carbon monoxide alarms are essential and why servicing should never be skipped.
Can a Boiler Gasket Be Replaced?
In many cases, yes. If the boiler is otherwise in good condition and parts are available, the failed gasket can be replaced and the combustion chamber resealed correctly.
After replacement, we:
- Reassemble using manufacturer approved components
- Torque seals to specification
- Re-test combustion
- Confirm safe flue gas readings
- Check for correct burner pressure
- Issue service documentation
If corrosion or heat damage has compromised other internal components, further repair or replacement may be recommended.
How Often Should Boilers Be Serviced?
Boilers should be serviced annually by a Gas Safe registered engineer. Regular servicing:
- Identifies safety issues before they escalate
- Prevents carbon monoxide risks
- Maintains manufacturer warranty
- Improves performance
- Extends appliance lifespan
Most gasket failures occur gradually due to heat cycling and material fatigue, meaning they are usually caught during routine maintenance rather than emergency breakdowns.
Professional Boiler Servicing and Safety Checks
At Alliance CFM, our engineers carry out thorough boiler servicing and safety inspections, including combustion analysis and internal seal checks. Identifying faults such as failed gaskets early prevents serious safety risks and avoids costly system damage later on.
If your boiler is due for a service or you are concerned about unusual smells, lockouts or carbon monoxide alarms activating, contact Alliance CFM to arrange an inspection. Call 0118 230 1268 or email contact@alliancecfm.co.uk!
