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COMMISSIONING: CO AND COMBUSTION RATIO CHECK
CO AND COMBUSTION
RATIO CHECK
First verify that flue
integrity has been
visually checked in
accordance with the
“Before CO and
combustion ratio check”
box (above) before
proceeding to the “Check
CO and combustion ratio
at maximum rate” stage.
SET BOILER TO MAXIMUM
RATE
In accordance with section 7.3-
7.4, set boiler to operate at
maximum rate (full load
condition). Allow sufficient
time for combustion to
stabilise.
CHECK CO AND COMBUSTION
RATIO AT MAXIMUM RATE
With boiler still set at maximum
rate, insert analyser probe into
flue gas sampling point. Allow
readings to stabilise before
recording.
Is CO less than
350ppm AND
CO/CO2 ratio
less than 0.004?
NO
Check all seals around the
appliance burner, internal flue
seals, door and case seals.
Rectify where necessary.
Is CO less than
350ppm AND
CO/CO2 ratio
less than 0.004?
CHECK CO AND
COMBUSTION RATIO AT
MINIMUM RATE
With boiler set at minimum
rate, insert analyser probe
into flue gas sampling point.
Allow readings to stabilise
before recording.
YES
Turn off appliance and
call Vokera technical
helpline for advice.
The appliance must not
be commissioned until
problems are identified
and resolved. If
commissioning cannot be
fully completed, the
appliance must be
disconnected from the
gas supply in accordance
with the GSIUR.
NOTE: Check and record CO
and combustion ratio at both
maximum AND minimum
rate before contacting
Vokera technical.
SET BOILER TO MINIMUM RATE
In accordance with section 7.3-
7.4, set boiler to operate at
minimum rate (to minimum
load condition). Allow sufficient
time for combustion to stabilise.
YES
Is CO less than
350ppm AND
CO/CO2 ratio less
than 0.004?
NO
Boiler is operating satisfactorily
No further actions required.
Ensure test points are capped, boiler case is correctly replaced and all other commissioning procedures are completed.
Complete Benchmark Checklist, recording CO and combustion ratio readings as required.
NOTE
The air/gas ratio valve is factory-set and
must not be adjusted during commissioning
unless this action is recommended, following
contact with Vokera technical. If any such
adjustment is recommended and further
checking of the boiler is required, the
engineer must be competent to carry out
this work and to use the flue gas analyser
accordingly. If the boiler requires conversion
to operate with a different gas family (e.g.,
conversion from natural gas to LPG) separate
guidance will be provided by Vokera
technical and must be followed.
NO
YES
BEFORE CO AND COMBUSTION RATIO CHECK
The boiler installation instructions should have been followed,
gas type verified and gas supply pressure/rate checked as
required prior to commissioning.
As part of the installation process, ESPECIALLY WHERE A FLUE
HAS BEEN FITTED BY PERSONS OTHER THAN THE BOILER
INSTALLER, visually check the integrity of the whole flue
system to confirm that all components are correctly
assembled, fixed and supported. Check that the maximum flue
lengths have not been exceeded and all guidance has been
followed (e.g. Technical Bulletin 008).
The flue gas analyser should be of the correct type, as specified
by BS 7967.
Before use, the flue gas analyser should have been maintained
and calibrated as specified by the manufacturer. The installer
must have the relevant competence for use of the analyser.
Check and zero the analyser IN FRESH AIR, as per analyser
manufacturer’s instructions.
