12.0
SERVICING AND MAINTENANCE
12.2
COMBUSTION CHECKS
COMBUSTION CHECKS AT MAXIMUM RATE
9. Set the boiler to Maximum gas rate.
10. Check the Carbon Monoxide (CO) and Carbon Dioxide (CO
2
)
readings are within the range quoted in the tables opposite
(Table 2).
11. If the combustion value(s) is outside the values specified
in Tables 1 and 2 and the integrity of the full flue system and
combustion circuit seals, the inlet gas pressure and gas rate
have been verified, it is possible to make an adjustment to the
combustion settings by adjustment of the air/gas ratio valve.
See Section 12.3 Adjustment of the Gas Valve.
30
© Dimplex Boilers 2008
12.3
ADJUSTMENT OF THE GAS/AIR RATIO VALVE
COMBUSTION SETTING ADJUSTMENT
1. It is only possible to adjust the valve at Maximum rate. No
adjustment at Minimum rate is allowed.
2. If the maximum rate setting is adjusted, then the
combustion values must be checked at minimum rate.
NOTE: DO NOT ATTEMPT TO ADJUST THE GAS/AIR RATIO
VALVE UNLESS;
• The person carrying out the measurement has been
assessed as competent in the use of a flue gas analyser
and the interpretation of the results.
• The flue gas analyser used, meets the requirements of
BS7927 or BS-EN50379-3.
• The flue gas analyser is calibrated in accordance with the
manufacturers requirements.
3. At Maximum Gas Rate; put the appliance into Service Mode
at Maximum Gas Rate (see Section 11.2).
4. Wait 5 minutes to allow the boiler to stabilise.
5. If the Carbon Dioxide (CO
2
) level is outside the required
values given in Section 12.2 (Table 2) then adjust the throttle
screw (Fig. 48) until the CO
2
is at the correct setting level. See
Table 4. Clockwise to decrease CO
2
, anti-clockwise to increase
CO
2
.
NOTE: Only turn the throttle in small steps of n
no more than
1/8
th
of a turn and wait 1 minute after each adjustment for
the combustion reading to stabilise.
IMPORTANT: After any adjustment of the gas valve, it is
essential to check the combustion levels at minimum gas
rate (Table 1). If the Carbon Monoxide or Carbon Dioxide
levels are outside the range quoted, call Dimplex Boilers Ltd
Technical Helpline on 0844 3711121. If in doubt ASK!
Table 4
Fig. 48
NOTE:
Factory set - warranty
void if adjusted
Throttle Adjuster Screw
Gas Valve
Inlet Test Point
Carbon Dioxide (CO2) acceptable setting level at Maximum
Gas Rate after 5 minutes operation
Natural Gas %
Boiler Model
Combi 24
9.0
10.7
Combi 30
9.3
10.9
Combi 38
9.1
10.7
LPG (Propane) %
8.0
FLUE OPTIONS
8.5
Kit C Horizontal Anti-Plume Flue Kit
(C13) - Part No. 956084
If the standard horizontal terminal is likely to cause nuisance to
a neighbour or buildings, because of excess pluming, then this
particular flue kit raises the flue gas outlet point to a higher
elevation with the minimum amount of changes. The flue gas
duct is teed-off from the concentric part and covered by an
80mm outer tube to protect the flue duct from freezing. The
air in-take remains at the lower level (see Fig. 24).
If choosing this option then the external flue duct length
should be taken into account when calculating equivalent flue
length.
For installation details refer to the flue kit instructions.
Dimensions from vertical terminals to opening windows should
be in line with Fig. 19.
(For use with Standard horizontal telescopic flue kit - Part no.
956120 - only).
This kit is provided to assist in fitting a condensing boiler with
reduced clearances when fitted in good practice according to
the Guide to Condensing Boiler Installation published by
DEFRA/HMSO.
This kit allows the boiler flue outlet to be directed to the left
or to the right only.
Suitable for installations if the appliance cannot be repositioned
and where other horizontal flue options may cause some
nuisance to neighbours or buildings. The flue kit contains some
additional 45° elbows and extension ducts as well as a special
wall bracket to pass the guttering (see Fig. 26). The concentric
flue will be routed vertically alongside the outside wall to
above the roofline. Special seals are required to prevent
rainwater penetrating the pipe joints.
For installation details refer to the flue kit instructions.
© Dimplex Boilers 2008
19
8.6
Plume Diverter Terminal Kit
Part No. 956103
8.7
Kit D External Vertical Flue
(C33) - Part no. 956085
93 flanged elbow (concentric)
with sampling point
Raised external flue outlet kit -
Part no. 956084
Kit C
Raised Ø60mm flue
outlet duct with
Ø80mm anti-freeze
pipe.
Max height of raised
flue from top of boiler
to centre of outlet 8.5m
Min height 1m.
Standard horizontal flue
adaptor has an already
built-in fall in the flue to
allow the condensate to
drain away.
93 flanged elbow (concentric)
with sampling point
Max. lengths (from top of
boiler to AIR COWL 8m
Min. length 1m.
Kit D
Ø60/100mm concentric
air/flue pipe -
Part no. 956093
(1m extension)
and
Part no, 956092
(0.5m extension)
For outside installations
the pipe joints have to
be covered with special
“lip-seal” to prevent
rain ingress.
Ensure all horizontally fitted
pipes are routed with a
2.5-3° fall towards the boiler.
External vertical flue kit - Part no. 956085
Roof terminal
with rain cover.
Roof terminal
with rain cover
and pitched roof
flashing kit.
b
a
8.4
Offset Vertical Flue Terminal
(C33) - HBL Part 956081
‘a’ measured from boiler flue outlet centre line to the centre
line of the extension elbow.
‘b’ measured from the top of the boiler to the underside of the
air cowl.
Maximum allowable length of a + b = 8900mm
Fig. 23
Fig. 24
Fig. 25
Fig. 26
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