Concealed flue ducts....
It has become fashionable amongst builders of flats and apartments to install
modern gas boilers with long ducts for the flues and air intakes concealed
behind ceilings or within the fabric of the buildings. This leads to a problem
that doesn't bother the builders, but it DOES affect any Gas Installer working
on the appliance at a later date. It's turning into quite a problem for either
Gas Installers or for their customers, depending on the attitude to risk of the
Gas installer, and I predict there will be a few high-profile court cases as a
The problem is this: Any gas installer working on a gas appliance is required
under regulation 26(7) of the Gas Safety (Installation and Use) Regulations 1998
to "examine the effectiveness of any flue" and "the supply of
combustion air". To comply with this regulation in practice we need to
inspect the whole of the flue length for integrity and make sure there are no
design and/or workmanship flaws, and do the same to the air intake duct. In many
properties, newly-built in particular, the flue and air ducts are concealed
behind ceilings or within the fabric of the building meaning this safety-check
cannot be done. The Gas Installer is obliged to 'condemn' the installation.
Now the chances of any individual flue duct or air intake being faulty are
quite small, so many Gas Installers take the view that they'll take a chance and
declare the appliance 'safe' despite being unable to inspect the flue and air
duct. In the vast majority of cases they will probably be right! But when the
Gas Installer works on large numbers of appliances then the risk of him/her
'passing' a genuinely dangerous flue becomes significant and the consequences
can be catastrophic, up to and including death of the occupier(s).
A flue duct that has come apart behind a ceiling void for example will be
discharging products of combustion onto the space behind the ceiling and these
potentially dangerous flue gases will be contaminating the air in the
house/flat. If the boiler then starts producing carbon monoxide the occupants of
the property will be at serious risk of CO poisoning and injury or death.
(Speculation is that this was the cause of death in the Oxford tragedy involving
two British Gas subcontractors who worked on a Range PowerMax boiler.)
When a flue or air intake duct is concealed and cannot be inspected the
appliance is, strictly speaking, categorised "At Risk" and should be turned
off and a Warning
Notice issued. Very tough if you called a boiler technician in to repair the
boiler in your smart new-build flat and he says 'no'. Sadly this is the
policy all Gas Installers need to follow to avoid risk to their customers and
personal prosecution with a potential prison sentence should such an event
The most common boilers to be installed with concealed flues and air intakes
are the Gledhill Gulfstream, the Range PowerMax, the Potterton PowerMax and the
Ideal Istor. Between them these four appliances are fitted in most gas-fired
new-build flats. Installations in new-build houses are less of a problem
- the ducts are not usually concealed in the same way as in flats.
CORGI recognised the extent of this problem and published a Technical
Bulletin TB200 (Link: TB200) defining details of a risk assessment that may be
carried out in lieu of visually inspecting the full length of a fanned flue
duct. Although the Risk Assessment is designed and developed by CORGI it is not
possible in my opinion for it to provide the definitive certainty about the
safety that a visual inspection will give. The only result a TB200 Risk
Assessment can deliver is an assessment of the likelihood of a
flue problem existing behind the concealing paneling. I always advise cutting
access holes for visual inspection. If the customer is unwilling to take that
step, a TB200 Risk Assessment is the appropriate action for the inspecting gas
technician to take.
Gas Safe Register have adopted the technical content of CORGI's TB200 and
re-issued it as Gas Safe Register Technical Bulletin 008.