Hearing an engineer say your boiler is condemned, or finding your boiler has been turned off, switched off and labelled, or marked at risk can be worrying—especially if you’re not sure what it means or what happens next.
This guide explains these terms in simple language, why they’re used, and what you should do if it happens to you.
If you need help or a second opinion, Trusted Boilers Ltd. can advise and carry out safe repairs or replacement where appropriate.
A Gas Safe engineer’s first job is safety. If a boiler (or any gas appliance) is found to be unsafe, the engineer may need to make it safe immediately. That can include the boiler being turned off or switched off and labelled to prevent use until the issue is fixed.
This doesn’t always mean you need a new boiler—but it does mean something needs attention.
When people say their boiler was condemned, they usually mean an engineer has identified a safety issue serious enough that the boiler should not be used.
In plain terms: “Boiler condemned” = “Do not use this appliance until it’s made safe.”
Sometimes it’s a repairable issue. Other times - especially with older boilers, repeated faults, or expensive parts—it may be more sensible to replace.
If you’re unsure, start with a professional assessment: Boiler repairs and diagnostics
If your boiler was turned off, it means the engineer has isolated it so it can’t run. This might happen if:
There’s a suspected flue problem
There’s a combustion/safety concern
If your boiler has been turned off, don’t try to switch it back on yourself. The safest next step is to have the fault properly diagnosed and repaired.
If your boiler was switched off and labelled, it means the engineer has attached a warning label to the appliance to make it clear it must not be used.
The label is there to protect you and anyone else in the property (family, tenants, future occupants), and it’s often used when the appliance is considered unsafe and needs repair or replacement before it can be used again.
If an engineer says your boiler is at risk, it usually means there is a safety concern that could become dangerous if left unresolved.
“Boiler at risk” can cover issues like:
Poor flueing or ventilation
Signs of incomplete combustion
Incorrect installation details
Deteriorating components that affect safe operation
In many cases, “at risk” situations can be resolved with the right repair work - but it should be treated as urgent.
Every situation is different, but unsafe findings often relate to:
Flue issues (damage, incorrect termination, poor seals)
Ventilation problems
Signs of carbon monoxide risk
Incorrect gas pressures or combustion readings
Unsafe pipework or installation defects
Appliance condition (age, corrosion, repeated lockouts)
If you’re experiencing repeated breakdowns or fault codes, it’s worth getting the boiler checked before it becomes a safety issue.Boiler servicing and maintenance
If your boiler has been condemned, turned off, switched off and labelled, or marked at risk, here’s the safest approach:
Don’t use the boiler until a qualified engineer confirms it’s safe
Ask what the issue is (and request it in writing if possible)
Arrange a proper diagnosis and quote for repair or replacement
If the boiler is older or repeatedly failing, consider replacement options
If you’d like Trusted Boilers to assess the situation, we can help you understand what’s going on and what your options are. Book a boiler repair
A repair may make sense if:
The boiler is relatively modern
The fault is clear and parts are available
The repair cost is reasonable
Replacement may be better if:
The boiler is 10+ years old
It’s breaking down regularly
Parts are expensive or hard to source
The safety issue is tied to age/condition or repeated failures
If replacement is the best route, you can explore options here: Combi boiler installation
If an engineer has turned your boiler off for safety reasons, you shouldn’t switch it back on until the fault has been properly diagnosed and a Gas Safe engineer confirms it’s safe. However, you are legally entitled to do so at your own risk.
Not always. Sometimes the issue is repairable. But if the boiler is older, parts are expensive, or faults are recurring, replacement can be the safer and more cost-effective option.
It means the boiler has been isolated and a warning label has been attached to make it clear the appliance must not be used until it’s made safe.
It usually means there’s a safety concern that could become dangerous if left unresolved. It should be treated as urgent, even if the boiler is still running.
Usually not. White steam (plumeing) on cold days is common with modern condensing boilers. However, if you notice unusual smells, dark smoke, staining, or repeated shutdowns, it’s best to get it checked.
Yes. Flue issues are a common reason appliances are marked unsafe, because the flue is responsible for safely removing combustion gases.
Treat it as urgent. Arrange an inspection and repair/replacement as soon as possible, and don’t allow the appliance to be used until it’s confirmed safe.
Trusted Boilers Ltd. supports homeowners and landlords across South London and North Surrey, including Wimbledon, Sutton, Banstead, Epsom, Croydon, and surrounding areas.
If you’re unsure what a label or warning means, or you need a safe repair or replacement plan, get in touch: Contact us