24
temperature increases, the temperature sensors
– located on the flow pipe of the boiler – reduce
the fan speed via the electronic circuitr y.
Depending on the load, either the water
temperature will continue to rise until the set point
is achieved or the water temperature will fall
whereby fan speed will increase relative to the
output required. When the boiler has reached the
set point (+ hysterisis), the burner will switch off.
The built-in anti-cycle device prevents the burner
from re-lighting for approximately 3-minutes. When
the temperature of the flow sensor falls below the
set point (- hysterisis), the burner will re-light.
NOTE
If the spark/sensing electrode does not sense
ignition the appliance will re-attempt ignition a
further 4-times then go to lockout. When the set-
point has been reached (the position of the heating
temperature selector) as measured at the primary
thermistor, the appliance will begin the modulation
phase whereby the fan and gas valve will
continuously modulate to maintain the set-point.
If the temperature continues to rise and exceeds
the set-point by 5°C (hysterisis), the burner will
shut down. A new ignition sequence will be enabled
when the 3- minute anti-cycle has been performed
and the temperature at the primary thermistor has
dropped 5°C (hysterisis) below the set-point.
7.2.5
DHW MODE
With the selector switch in either the hot water
only or heating & hot water position, the appliance
will operate in the hot water mode whenever a
DHW outlet is opened. A flow rate exceeding 2-
litres per minute will activate the DHW flow switch
whereupon the pump and fan will be activated via
the flow temperature sensor. When the fan is
sensed to be operating correctly (tacho signal),
the ignition sequence commences. Ignition is
sensed by the electronic circuitry to ensure flame
stability at the burner. Once successful ignition
has been achieved, the electronic circuit allows
the gas rate to achieve the modulation value.
NOTES
When the request for heating and/or hot water has
been satisfied, the appliance pump and fan may
continue to circulate to dissipate any residual heat
within the appliance.
7.3
APPLIANCE FAN SPEEDS
The appliance fan speeds require to be checked
and/or adjusted prior to making any adjustments
to the gas valve or if the main PCB has been
replaced.
ATTENTION
Gas type and appliance fan speed (output)
must
be set
according to the specific appliance
specification. Vokera accepts no responsibility if
the gas type and/or fan speed is not correctly
adjusted according to the respective appliance
specification as detailed on the appliance data
badge.
7.3.1
CHECKING/ADJUSTING THE APPLIANCE FAN
SPEEDS
Move the selector switch to the OFF position and
remove the 3-selector knobs.
7.3.2
ABSOLUTE MAX FAN SPEED
Locate the MAX trimmer (fig. 36) and gently adjust
clockwise or counter clockwise to achieve the
correct fan speed (see table 7.3.6). NOTE, the
display shows the fan RPM in multiples of 1000,
i.e. 2.5 = 2500RPM.
7.3.3
ABSOLUTE MIN FAN SPEED
Locate the MIN trimmer (fig. 36) and gently adjust
clockwise or counter clockwise to achieve the
correct fan speed (see table 7.3.6). NOTE, the
display shows the fan RPM in multiples of 1000,
i.e. 2.5 = 2500RPM.
7.3.4
IGNITION FAN SPEED
Locate the IGN trimmer (fig. 36) and gently adjust
clockwise or counter clockwise to achieve the
correct fan speed (see table 7.3.6). NOTE, the
display shows the fan RPM in multiples of 1000,
i.e. 2.5 = 2500RPM.
7.3.5
HEATING FAN SPEED
Locate the HTG trimmer (fig. 36) and gently adjust
clockwise or counter clockwise to achieve the
correct fan speed (see table 7.3.6). NOTE, the
display shows the fan RPM in multiples of 1000,
i.e. 2.5 = 2500RPM.
fig. 36
7.3.6
FAN SPEED TABLE
Use the following table to set the corresponding
fan speeds that are relative to the appliance you
are working on.
FAN SPEED (rpm) TABLE
MODEL
MAX
MIN
HTG
IGN
28HE
6100
1700
4400
3700
32HE
5900
1500
4500
3700
36HE
6300
1400
5200
3700
7.4
CHECKING THE CO
2
AND ADJUSTING THE
GAS VALVE
THE GAS VALVE MUST BE SET-UP OR
ADJUSTED WITH THE AID OF A PROPERLY
CALIBRATED FLUE GAS ANALYSER.
Isolate the appliance from the electrical supply
and remove the appliance casing as described in
4.7.1. Set the flue gas analyser to read CO
2
and
insert the probe into the flue analysis test point (
A,
B
fig. 35). Restore the electrical supply to the
boiler and switch the boiler to the OFF mode. To
adjust the gas valve you must first ensure that the
fan speed potentiometers (trimmers) have been
set correctly (see 7.3).
Remove the 3-selector knobs, locate and press
the CO button (see fig. 36). The appliance will now
operate in CO mode for approximately 15-minutes
(see 7.10).
7.4.1
GAS VALVE MAXIMUM SETTING
Locate and gently turn the HTG trimmer till the
maximum value fan speed (max) is obtained and
check that it corresponds with the appropriate CO
2
value (Maximum) for the respective appliance. If
the CO
2
reading is correct, proceed to gas valve
minimum setting (7.4.2).
However, If the CO
2
reading is incorrect, the
maximum gas pressure must be adjusted as
follows:
•
Using a 2.5mm Allen key, very slowly turn the
maximum adjustment screw (see fig. 37) –
clockwise to decrease, counter clockwise to
increase – until the correct value is displayed on
the CO
2
analyser (allow time for the analyser to
stabilise).
