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7.6
SETTING THE AIR/GAS RATIO
NOTICE: THE SETTING OF THE GAS RATIO MUST BE
CARRIED OUT BY A COMPETENT PERSON. SETTING OF
THE GAS RATIO MUST NOT BE ATTEMPTED UNLESS
THE PERSON CARRYING OUT THE TEST IS EQUIPPED
WITH A COMBUSTION ANALYSER CONFORMING TO BS
7927 AND IS COMPETENT IN ITS USE.
7.6.1
Setting the CO/CO
2
▶ Refer to section 7.2 and ensure that the gas inlet pressure is correct
before continuing.
▶ To adjust the CO/CO
it will be necessary to first operate the
2
appliance at maximum output.
▶ Refer to section 7.4 for setting the appliance to maximum and
minimum output.
▶ Refer to table 34 and check the CO/CO
the maximum CO/CO
via adjuster (1) on the gas valve using a
2
2.5mm Allen key.
▶ Check CO is less than 200ppm.
▶ Set the control to minimum (MIN).
▶ The appliance will go to minimum power.
▶ Measure the CO/CO
and check against table 34.
2
If required set the minimum CO/CO
until the correct measurement is set:
– Remove dust cap with flat bladed screw driver.
– Using a 4mm Allen key adjust CO
– Replace the dust cap.
▶ Check that the CO is less than 200ppm.
▶ Return the appliance control to maximum and re-check the CO/CO
If correct, set the appliance control to normal "NORM".
▶ Re-fit the control cover
▶ Re-fit appliance outer case.
MAX
1
2.5 mm
MIN
2
4 mm
Fig. 57 Gas valve adjustment
CO/CO
values
2
CO/CO
should be measured after 10 minutes.
2
Gas type
Natural gas: 9 - 21kW outputs
Natural gas: 24kW output
LPG: All outputs
NOTE: When checking an existing appliance the tolerance is ± 0.5.
If checking after cleaning or component replacement or for adjustment
when the reading obtained is outside the tolerances given above, then
the tolerance is ± 0.2.
CO - less than 200 ppm (0.002 ratio)
Table 34 CO/CO
settings
2
6 720 821 670 (2018/06)
at maximum. If required set
2
via adjuster (2) on the gas valve
2
.
2
.
2
6720643895-66.1Wo
CO
max.
CO
min.
2
2
9.6% ± 0.5
8.6% ± 0.5
9.55% ± 0.5
8.55% ± 0.5
10.5% ± 0.5
10% ± 0.5
7.7
CLEANING THE HEAT EXCHANGER
NOTICE: COMBUSTION TESTING
▶ Combustion testing must be carried out by a
competent person. Testing must not be attempted
unless the person carrying out the combustion check
is equipped with a Combustion Analyser conforming
to BS 7927 and is competent in its use.
NOTICE: CO/CO
CHECKS
2
▶ If the joint between the Air/Gas manifold and heat
exchanger is disturbed, replace the sealing gasket.
▶ After completing the service of the appliance, the
CO/CO
must be checked and set to the limits shown
2
in "Setting the air/gas ratio" on page 47.
There is a special accessory kit available specifically
designed for cleaning the heat exchanger. If required
order 7 716 192 312.
▶ Isolate the power to the appliance and remove outer case and base
panel.
1. Refer to figure 58 and remove the clip from gas valve outlet.
If the plastic elbow can not be easily removed, undo the
nut to push the plastic elbow out of the fitting.
2. Pull the gas outlet elbow free from the gas valve.
2.
Fig. 58 Gas valve connection
▶ Remove electrical connector and earth wire from fan.
To prevent damage to the electrodes when removing the
air/gas manifold, disconnect the leads to the electrodes.
▶ Disconnect spark electrode and flame sensor connections.
1. Refer to figure 59 and undo the securing nut on the top of the heat
exchanger and remove the retaining plate assembly.
Fig. 59 Securing nut
SERVICE AND SPARES
1.
6720643895-72.1Wo
1.
47
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