Flues In Voids FAQs

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If your gas engineer cannot examine the whole length of the flue they will advise you, in line with industry guidance, that it is 'At Risk', recommend that you do not use it and will ask your permission to turn it off. This is assuming that there are no other indications that your boiler is not safe, regardless of the unknown condition of the flue.

'At Risk' is a risk classification used by gas engineers and means that your boiler and flue system could become dangerous in the future, in this case it is used because the engineer cannot examine the length of the flue to confirm it is safe. As a consumer you are within your rights to refuse permission for it to be turned off, however you will be asked to sign paperwork to confirm you accept responsibility for those defects identified in the system – in this case, the potential for fumes to escape unnoticed from the concealed flue into the property. Your gas engineer can continue to work on your boiler including servicing it and undertaking maintenance work.

If you have had your boiler serviced since January 2011, your gas engineer should have made you aware of the need for inspection hatches, giving you time to consider what action to take.


The law has not changed. What has changed is guidance to gas engineers in relation to them being able to examine the flue. There is no legal duty on you to have inspection hatches or other controls installed. If you choose not to have them, you should continue to have your boiler serviced and checked every year by a Gas Safe registered engineer who will advise that it is ‘At Risk’ (see above).

If you choose not to have inspection hatches fitted, industry has developed a safety system which can monitor the void through which the flue runs for carbon monoxide. This system will cause the boiler to be shutdown if and when carbon monoxide is detected. Your registered gas engineer will be able to provide you with further information on these systems. Inspection hatches remain the preferred option but the safety shut down system does afford you with a level of protection against an undetected failure of the flue.

Fitting carbon monoxide alarms are also a good second line of defence but are no replacement for an engineer being able to fully inspect the complete flue.


You are required, by law, to have an annual gas safety check carried out, by a registered engineer, on every gas appliance you provide and on any flue/chimney. Additionally landlords are required to ensure that gas fittings and flues are maintained in a safe condition. These duties require the gas engineer to be able to examine the flue to check that it is safe. Repositioning the boiler or the flue is an option, but if this is not viable, inspection hatches are currently the recommended means by which an engineer can adequately examine along the length of a concealed flue.

Visual examination checks by engineers via inspection hatches is currently the preferred method recommended by the industry guidance that explains how to judge that a flue is working safely and effectively. However, where inspection hatches are not practicable industry has developed a safety system which is able to monitor the void for the presence of carbon monoxide and which cause the boiler to shut down if it is detected.

Speak to your Gas Safe registered engineer for advice on what solution may be appropriate for you.

Advances in technology allowed boilers to be put in a greater variety of positions, not just on an outside wall, suiting the development of flats and apartments where space was at a premium. This resulted in some room sealed boilers being installed in a way that the flue cannot be examined to make sure it is correctly fitted and safe.

No. There is no legal duty on the consumer to have inspection hatches installed. However, there is a long-standing legal duty on gas engineers to be able to examine the flue to ensure it is safe whenever they work on your boiler. In the majority of cases this will be only be possible though the installation of inspection hatches. If gas engineers cannot examine the flue along its length they will advise you that the installation is ‘At Risk’ and will seek your permission to turn it off.

It is important that this should not deter you from having your boilers serviced or maintained as this will at least confirm that the boiler itself is currently safe even if the flue cannot be confirmed as safe.


It will vary from property to property. It is recommended that hatches are at least 300mm x 300mm and wherever possible, be positioned within 1.5m to the side of any joint in the flue system. Therefore, some properties will only need one hatch, while others may need more.

Basic inspection hatches must comply with the Building Regulations and are likely to cost from £75, though you may choose to fit more expensive ones for cosmetic reasons. Costs for the fitting of the inspection hatches will be extra.


If your flue could not be examined, your gas engineer should have informed you on a previous visit that your system was ‘Not to Current Standards’, unless there was evidence of an additional safety issue that would have required your boiler system to be declared ‘Immediately Dangerous’.

Technical instructions to gas engineers changed from January 2011 following a number of cases where, once inspection hatches had been installed, faults were found in flue systems. There have also been several cases where CO from a faulty boiler has been found to be entering properties from faulty concealed flues. In light of this evidence, industry organisations have now decided it is right for gas engineers to classify installations with concealed flues as ‘At Risk’ for the safety of the occupants.

When you purchased the property your solicitor should have told you who was providing the home warranty. It is possible that you have correspondence from the warranty provider. The main warranty providers in the UK are NHBC, Premier Guarantee and Checkmate. Depending on the age of the property Zurich Building Guarantee may have provided the warranty.

If your home warranty has expired, you or your landlord will have to meet the cost of the inspection hatches and any defects to the boiler or its flue. If you receive benefits you may be entitled to financial assistance. Further details can be found on the Health and Safety Executive website.

It may still be worth contacting your home builder who may be willing to assist in some way, or be able to recommend reputable building services companies to carry out the work.

A competent builder or building services company should be able to fit the inspection hatches. The builder will need to speak to a registered gas engineer on how many inspection hatches are needed and where they should be located.

If you do not know a builder, the government supported ‘Trustmark’ scheme should be able to provide advice on how to find a reputable building company to carry out the work. Go to trustmark.org.uk or call 0333 555 1234 for further details.

It is possible that the original plasterboard ceiling will have been designed to provide fire protection; it may also provide acoustic/noise protection too. The hatches that are fitted need to provide equivalent fire/noise protection to the ceiling they are replacing. Fire-rated hatches are more expensive than non-fire rated budget ones. When retro-fitting inspection hatches it is recommended that hatches rated to provide a minimum of 1-hour fire resistance should be specified. Non-fire rated hatches should only be fitted where professional advice has confirmed they are suitable - such advice may be available from the original builder or a suitably qualified surveyor.

Note: Where advice is not freely available from the original builder it may well be cheaper to fit 1-hour fire-rated hatches than to pay for professional advice to determine whether or not they are required.

Inspection hatches installed to provide access to an existing chimney system in a void in the majority of cases should usually have a minimum of one hour fire resistance for residential buildings with floors no higher than 18m above ground level. The use of non-fire rated hatches needs to be assessed by a suitably qualified surveyor to ensure satisfactory fire and acoustic resisting performance.

The following bullet points may provide additional help in determining the type of inspection hatches you may need:

  • Two storey houses and those with fire escape stairs require robust fire resisting floors and escape routes that usually rely on the internal linings to maintain integrity for the required length of time. A fire resisting hatch of some type will usually be required in these situations.
  • In apartments with concrete or timber floors, the plasterboard ceiling below could be providing fire resisting properties to either the structural elements or the protected escape routes. In most situations the suspended plasterboard ceiling will have been an integral part of the assessed acoustic performance, any hatches within it will need to maintain satisfactory acoustic performance. A denser fire rated hatch should provide better acoustic performance than a non-rated hatch. Therefore in most apartment block situations a rated hatch is either required or is beneficial.
  • The majority of installations would normally be covered by the above, but there may be other situations where non-rated hatches can be used. This will require an assessment from someone that is suitably qualified and understands the technical aspects of the building.

In all cases the inspection hatch manufacturer will be able to confirm the fire resistance and provide a fire test certificate. In new build situations, the building control body will be able to advise on the suitability of the inspection hatches.

Where the flue also passes through a neighbouring property the engineer should take all reasonable steps to ensure overall flue integrity. This will involve making enquiries with the occupants of the neighbouring property. In these situations and on the basis of checks of the boiler and the chimney/flue system in the property containing the boiler are all satisfactory, reasonable steps need to be taken to gain access to adjacent property to check overall chimney/flue system integrity. Gaining access to adjacent property will normally require the full assistance and co-operation of others to achieve e.g. Housing Associations, Social Landlords and neighbours etc. Reasonable steps may be demonstrated by taking the following actions as a minimum:

  • making enquiries with the occupants of those other adjacent properties to gain access.
  • writing to the occupier explaining the requirement and seeking arrangements to gain access within a reasonable timescale.
  • making arrangements for suitable access to be provided within a reasonable timescale.

In some cases, despite having taken reasonable steps, access to the flue in the neighbouring property may not be possible (e.g. hatches not fitted within neighbouring property or a lack of response from occupier). When the engineer checks the flue in the property where the appliance is located there is no evidence of concern, then having taken reasonable steps to access the adjoining property (but failed) the engineer’s risk assessment can conclude (with the appliance remaining operational). However where the engineer has good reasons to suspect flueing problems it is essential that the complete length of the flue is checked (including adjoining property) and the appliance must not be used unless or until this is done.

The aim of this guidance is to make consumers aware of important safety issues relating to concealed room sealed flue systems and carbon monoxide and to set out what action should be taken to protect those who live in or visit the property. As a consumer you are free to refuse the gas engineer permission to turn off your boiler. In these circumstances however you will be asked to sign paperwork to confirm you accept responsibility for those defects identified in the system which could result in a serious incident.