An engineer has put a 'Danger Do Not Use' label on your boiler, switched it off and asked you to sign a form. In the middle of a Scottish winter that's unsettling, and it raises three questions: is it really that bad, am I allowed to use it, and do I need a new boiler?
'Condemned' isn't an official term. What has happened is that a Gas Safe registered engineer has found a fault and followed the industry's unsafe situations procedure. This guide explains the classifications, what the engineer must do, where you stand legally, how to get a second opinion and how to judge repair against replacement.
If you can smell gas right now, call the National Gas Emergency Service on 0800 111 999.
The short answer
- Under the Gas Industry Unsafe Situations Procedure (IGEM/G/11), an unsafe appliance is Immediately Dangerous (ID) or At Risk (AR). 'Not to Current Standards' is no longer an unsafe category.
- With your permission, an ID appliance is disconnected and sealed off; an AR appliance is turned off. Both get a 'Danger Do Not Use' label and a warning notice.
- Once you've been told it's unsafe, using it or letting anyone else use it can be an offence under regulation 34 of the Gas Safety (Installation and Use) Regulations 1998.
- Refuse disconnection of an ID appliance and the engineer will report it to the gas emergency service, which has powers to make it safe.
- You can ask for the reason in writing and have a second Gas Safe engineer check it. Keep it off meanwhile.
- A flue joint, ventilation or a failed part is often repairable. A failed heat exchanger on an older boiler often means replacement.
What does 'condemned' actually mean?
Gas Safe registered engineers follow the Gas Industry Unsafe Situations Procedure, published by the Institution of Gas Engineers and Managers as IGEM/G/11. The current version is Edition 2, last amended in July 2025. It sets out how unsafe appliances and installations are classified and what the engineer must do about each. There are two classifications, and both mean the appliance must not be used.
- Meaning. Immediately Dangerous (ID): A danger to life or property now, if left connected to the gas. At Risk (AR): One or more faults that could make it dangerous in use.
- Examples. Immediately Dangerous (ID): Gas escape, fumes spilling into the room, a disabled safety device. At Risk (AR): Damaged or poorly supported flue, inadequate ventilation.
- Made safe by (with your permission). Immediately Dangerous (ID): Disconnecting it and sealing the gas supply. At Risk (AR): Turning it off at the gas isolation valve and electrical supply.
- Label and paperwork. Immediately Dangerous (ID): 'Danger Do Not Use' label and warning notice. At Risk (AR): 'Danger Do Not Use' label and warning notice.
What happened to 'Not to Current Standards'?
Older paperwork may show a third category, Not to Current Standards (NCS). It was dropped from the unsafe situations procedure in 2015 because those situations aren't unsafe. An engineer can still note that something falls short of today's standards, but it won't get a warning label. If your form says NCS, your appliance hasn't been condemned.
When switching off wouldn't help
A few At Risk situations can't be made safer by turning an appliance off, such as an emergency control valve nobody can reach or a gas service pipe that has been built over. There's no 'Do Not Use' label in those cases. The warning notice tells you who needs to be contacted to put it right instead.
What the engineer has to do
- Fix it there and then if possible. If the fault can be safely put right during the visit and you agree, that comes first.
- Explain the classification, why it applies and that the appliance must not be used.
- Make it safe. Disconnect and seal an ID appliance; turn off an AR appliance at the gas valve and the electrical supply. Turning the thermostat down or the timer off doesn't count.
- Label it prominently with a 'Danger Do Not Use' label showing the engineer's name, registration number and the fault.
- Issue a warning notice recording the fault, classification, action taken and what's needed to fix it. You sign to confirm receipt and keep a copy.
- Tell the owner. If you rent, the landlord or managing agent must get the details in writing.
- Record any refusal to allow the appliance to be made safe, or to sign.
If nobody is home, the engineer should still make it safe and leave the notice on site. They must be able to justify the classification, so ask to see the fault or the readings.
What if you refuse?
An engineer can't legally disconnect your appliance against your wishes, but the duty not to use an unsafe appliance stays with you. For an Immediately Dangerous appliance, if you refuse disconnection the engineer will try to turn it off and then report it to the Gas Emergency Contact Centre on 0800 111 999. The gas emergency service has powers under the Gas Safety (Rights of Entry) Regulations to enter premises and make an installation safe. For an At Risk appliance, your refusal is recorded and continued use is your responsibility.
Is it illegal to use a condemned boiler?
Regulation 34 of the Gas Safety (Installation and Use) Regulations 1998 says the responsible person for a property (the occupier, owner, or anyone with authority over the gas fittings) must not use a gas appliance, or allow it to be used, if they know or suspect it can't be used without danger. A warning notice gives you that knowledge. HSE's guidance puts it plainly: using a gas appliance you suspect is unsafe is illegal.
- Don't reconnect it or turn it back on. That's gas work, and by law only a Gas Safe registered engineer can do it.
- Leave the label in place. It warns family, tenants, staff and visitors. Removing it doesn't change the classification or your legal position. It should come off once a Gas Safe engineer has fixed the fault and tested the appliance as safe.
- Signing the notice only confirms you received it. It doesn't stop you getting a second opinion.
What the RIDDOR box means
Under regulation 11(2) of RIDDOR 2013, a Gas Safe registered business must report to HSE, within 14 days, any gas fitting it considers dangerous enough to cause death, loss of consciousness or hospital treatment because of how it was designed, installed, altered or serviced. That covers leaks, fumes and poor flueing. A fitting that's dangerous only through lack of maintenance isn't reportable, and fixing it on the same visit doesn't remove the duty. The report is the engineer's job, not yours.
If you smell gas or suspect carbon monoxide
Smell gas? Open doors and windows, turn off the gas at the meter if you can, and call 0800 111 999. Don't smoke or use a naked flame, don't operate electrical switches, and don't go into a cellar.
Carbon monoxide has no smell. Symptoms include headaches, dizziness, nausea, tiredness, confusion, breathlessness and chest or muscle pain, often easing when you leave the building. Turn the appliance off if it's safe to, get into fresh air, call 0800 111 999 and get medical advice from NHS 24 on 111. Call 999 if someone is struggling to breathe, confused or unconscious.
In Scotland, every home with a carbon-fuelled appliance such as a boiler, gas fire or flue must have a carbon monoxide detector.
Landlords and tenants
Regulation 36 requires landlords to keep the gas appliances, flues and pipework they provide in a safe condition, and Scotland's Repairing Standard requires gas, heating and hot water installations to be in reasonable repair and proper working order. A warning notice on a tenant's boiler needs dealing with promptly.
- The tenant must not use it. Tenants have their own duty not to use an appliance they believe is dangerous, and a landlord must never ask them to carry on until the engineer returns.
- Emergency heating. HSE guidance says that where a heating appliance has been disconnected, the landlord must provide emergency heating while a Gas Safe engineer arranges the repair.
- It's on the record. Defects and remedial action appear on the landlord gas safety record.
Private tenants whose landlord doesn't act can apply to the First-tier Tribunal for Scotland (Housing and Property Chamber). For annual checks, see our landlord gas safety certificate guide.
Common reasons appliances are classed as ID or AR
This is how IGEM/G/11 typically treats common faults. The engineer's classification always depends on exactly what they find.
- Gas escape (failed tightness test or smell of gas). Typical classification: Immediately Dangerous. Usually repairable?: Usually, once the leak is found.
- Fumes spilling from the flue, or signs of spillage. Typical classification: Immediately Dangerous. Usually repairable?: Depends on the cause; often a flue or ventilation fix.
- Flue damaged, unsupported or with unsealed joints. Typical classification: At Risk; ID if fumes are entering the building. Usually repairable?: Often.
- Missing, undersized or blocked ventilation. Typical classification: At Risk. Usually repairable?: Usually.
- Cracked heat exchanger or leaking case seal. Typical classification: At Risk; ID where fumes are escaping. Usually repairable?: Seals yes; a failed heat exchanger on an older boiler often means replacement.
- Safety device bypassed or not working. Typical classification: Immediately Dangerous. Usually repairable?: Usually, by replacing the part.
- Poor combustion (high carbon monoxide readings). Typical classification: At Risk on a flued boiler; ID on a flueless appliance or with CO in the room. Usually repairable?: Often, with a service or repair.
- Open-flued or flueless appliance in a bathroom. Typical classification: Immediately Dangerous. Usually repairable?: Normally means removal or replacement.
In Glasgow tenements and ex-council flats, common culprits are vents blocked up to stop draughts, boilers boxed into cupboards without the ventilation their manual requires, and old open-flued gas fires or back boilers.
Can you get a second opinion on a condemned boiler?
Yes. HSE's advice is to follow the first engineer's advice in the meantime, so the appliance stays off while you do.
- Read the warning notice. If the fault description is vague, ask the engineer's company to set out the reason in writing, with readings or photos.
- Check the engineer's Gas Safe ID card, which shows the appliance types they're qualified for. You can verify it on the Gas Safe Register website.
- Book a second Gas Safe engineer and give them the notice. They should carry out their own checks.
- Raise concerns with the Gas Safe Register if you believe the classification or work was wrong.
If the fault is real, a second engineer will classify it the same way. Where a second opinion genuinely helps is the next step: whether it's a straightforward repair or really does mean a new boiler.
Repair or replace?
A warning notice doesn't automatically mean a new boiler. Resealing a flue joint, adding a flue support, clearing or fitting a vent, fixing a leaking gas fitting, replacing a faulty safety device, fan or case seal, or servicing a boiler that's burning poorly are all common repairs.
Replacement is usually the sensible choice when the heat exchanger has failed on an older boiler, parts are obsolete, the flue can't meet the manufacturer's requirements where it is, or the appliance isn't permitted where it's fitted. A useful rule of thumb: if the repair costs more than half the price of a new boiler and the boiler is over ten years old, replacing it usually makes more sense. See our guides to boiler repair costs in Glasgow and new boiler costs in Glasgow and Lanarkshire.
If you don't plan to repair or replace a condemned appliance, such as an old gas fire, have it properly capped off by a Gas Safe engineer rather than leaving it behind a label.
Business premises: plant rooms, warm air heaters and kitchens
The same classifications apply in commercial buildings, and regulation 35 requires employers to keep workplace gas appliances, flues and pipework safe. Because shutting gas plant down can affect a building or process, the procedure leaves the decision on how and when to shut down with the responsible person on site.
Plant rooms and commercial boilers
Common findings are plant room ventilation that doesn't meet the manufacturer's requirements or BS 6644, flue defects and, on fan-diluted flues, readings above 1% carbon dioxide or 50 ppm carbon monoxide, which are At Risk. One ventilation or flue fault can affect several boilers, so check the notice lists every appliance it covers. See our commercial boiler repair service.
Warm air heaters
On indirect-fired heaters, a cracked heat exchanger can let carbon monoxide into the air blown around the building and normally means replacing the heat exchanger or heater. An unsealed plenum is Immediately Dangerous where it affects safe operation, and a missing return air path is At Risk. More in our warm air heater servicing guide.
Commercial kitchens
The engineer checks the interlock that should cut the gas if extraction fails. HSE says manual bypasses aren't permitted. BS 6173 isn't retrospective, so an older kitchen without an interlock isn't automatically condemned, but the risk must be assessed and controlled. Missing flame supervision on ovens and burners is another common reason for an unsafe classification. See our guide to commercial kitchen gas safety certificates (CP42).
How Titan Heat can help
If a boiler or gas appliance in your home has been labelled 'Danger Do Not Use', book a repair visit. The £85 fixed call-out covers the visit and diagnosis; we'll check the fault against the warning notice, explain what we find and give you a fixed price for the repair before any work starts. If replacement makes more sense we'll explain why, and you can request a new boiler quote. Installs start from £2,500 and our work carries a 1-year parts and labour guarantee.
Titan Heat is Gas Safe registered (982732) and covers Glasgow, Lanarkshire, Renfrewshire, East Renfrewshire and East and West Dunbartonshire. Same-day emergency boiler repairs are subject to engineer availability.
For commercial boilers, plant rooms and warm air heaters across Glasgow, Lanarkshire and Central Scotland, Stephen holds commercial ACS qualifications including indirect-fired appliances (CIGA1). Send us the warning notice through our commercial enquiry form.
Frequently asked questions
Can a gas engineer condemn my boiler without my permission?
They can classify it, label it and issue a warning notice without your agreement. They need your permission to disconnect it or turn it off, but if you refuse on an Immediately Dangerous appliance they'll report it to the gas emergency service, which has powers to make it safe.
Is it illegal to use a boiler with a warning notice on it?
Once you've been told it's unsafe, using it or allowing it to be used can be an offence under regulation 34 of the Gas Safety (Installation and Use) Regulations 1998. That applies to both ID and AR appliances.
What's the difference between Immediately Dangerous and At Risk?
Immediately Dangerous means a danger now if left connected, so it's disconnected. At Risk means faults that could become dangerous in use, so it's turned off. Neither should be used.
Can I remove the 'Danger Do Not Use' sticker?
Leave it until a Gas Safe registered engineer has fixed the fault and confirmed the appliance is safe. Turning the gas back on or reconnecting is gas work only a registered engineer can legally do.
My landlord's boiler has been condemned. What happens now?
Don't use it. Your landlord must arrange the repair or replacement and, under HSE guidance, provide emergency heating in the meantime. Private tenants can apply to the First-tier Tribunal for Scotland if the landlord doesn't act.
Does a condemned boiler always need replacing?
No. Flue, ventilation and component faults are often repairable. Replacement usually makes more sense when an older boiler's heat exchanger has failed, parts are obsolete, or the repair costs more than half the price of a new boiler.
