Gas boilers - flues in voids


Gas engineers are legally required to check the flue after installing or carrying out any work on boilers.This site provides additional information on related issues.


The introduction of fan-flued gas appliances in the mid 1990s allowed gas central heating boilers to be installed away from external walls. This meant that builders could design new-build and refurbishment properties with boilers installed on internal walls to make better use of the available space. The flues to these boilers were, in some cases, routed through voids in the ceiling space or through stud walls within or between properties.

Gas engineers are legally required to check the flue after installing or carrying out any work on the boiler. This includes a visual inspection. The original installer and every subsequent service or maintenance engineer needs to be able to check that:

  • the flue is continuous throughout its length
  • all joints are correctly assembled and are appropriately sealed
  • the flue is adequately supported throughout its length

Unless the gas engineer can make these checks they cannot ensure that the flue from the boiler complies with statutory requirements and therefore is safe. This necessitates the provision of appropriate inspection hatches.

Where a flue fault exists in combination with a boiler which is not operating correctly, dangerous levels of carbon monoxide (CO) could be released into the living accommodation.

Safety notice

The Health and Safety Executive (HSE) issued a safety alert on 2nd October 2008 following a death earlier that year. An updated safety notice was issued by HSE in December 2010 and subsequently updated again in May 2013.

The purpose of the original alert in 2008 was to raise awareness of the potential dangers from certain types of flues connected to gas-fired central heating installations in some properties (particularly, but not exclusively, a large number of flats and apartments completed since about 2000) that may not have been installed properly, or may have fallen into disrepair.

The 2008 alert referred to the relevant gas industry technical guidance which gas engineers were expected to follow. A revised version of this guidance has now been published by Gas Safe Register. This changes the approach that Gas Safe registered engineers will take when they encounter relevant installations.

Action required

The revised technical guidance (TB008) requires inspection hatches to be fitted in properties where the flue is concealed within voids and cannot be inspected. The homeowner (or landlord etc.) has to arrange for inspection hatches to be installed. Any gas engineer working on affected systems will advise the homeowner that the system is "at risk" (AR) in accordance with the Gas Industry Unsafe Situation Procedure (GIUSP) and, with the owner's permission will turn off the gas supply to the boiler so it cannot be used.

Once inspection hatches have been fitted, the gas engineer will be able to make sure that the flue is safe and was installed in line with the relevant standards and manufacturers instructions.

Further information

Information for consumers, including a list of Questions and Answers, can be found by visiting the Gas Safe Register website. For additional enquires not answered through these routes please send questions to:

Further information is available from HSENI’s gas safety unit on 0800 0320 121 or via email to


​Please note that this link is to the original legislation, visitors should verify for themselves whether legislation is in force or whether it has been amended or repealed by subsequent legislation.