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7.1 CHECKING APPLIANCE OPERATION
When carrying out any repairs or servicing to the ap-
pliance, the relevant commissioning procedure must be
undertaken to ensure the continued safe operation of the
appliance. Particular attention should be made to ensure
gas soundness, water soundness, and the electrical
integrity of the appliance.
7.2 APPLIANCE MODES OF OPERATION
NOTE
The 2-digit display can show several different modes of
operation:
OFF
mode
Frost protection mode active
Combustion analysis mode active
Autostop function active
Normal heating request (example 60
o
C).
Purge cycle mode.
SECTION 7 CHECKS, ADJUSTMENTS AND FAULT FINDING
7.2.1 SELECTOR SWITCH IN THE OFF/STANDBY
POSITION
When the selector switch is in the OFF/STANDBY posi-
tion, the following functions are active.
Active functions
:
Frost-protection system
Pump anti-block
7.2.2 ON-BOARD FUNCTIONS
AUTOSTOP:
Further information on the AUTOSTOP
function, can be obtained from your local Vokera Sales
Representative.
CO FUNCTION:
The CO function when activated, will
allow the appliance to run at maximum and minimum
output whilst a combustion analysis check is being
carried out. Whilst the CO function is active, all other
functions are disabled (minimum power operating pe-
riod, anti-cycle, set-point, etc). Once enabled, the CO
function will remain active for a 15-minute period, or
until the function is manually deactivated
FROST-PROTECTION:
this function is only active
when there are no requests for heating or HW. If the
temperature drops below 5°C, the boiler will operate
on minimum power until the temperature of the primary
thermistor reaches 35°C. Thereafter the pump & fan will
over-run for fi ve minutes.
ANTI-CYCLE FUNCTION:
The anti-cycle function
ensures the burner remains switched off for at least
5-minutes after the set-point hysterisis (set-point + 2
-8 °C).
PUMP ANTI-BLOCK FUNCTION:
when there has
been no heating or HW request for 24-hours, the anti-
block cycle is activated. The pump will be activated for
a period of 30-seconds.
PUMP DISCHARGE FUNCTION:
at the end of any
power on, the boiler makes an ON/OFF pump cycle
(about 2 minutes). Only at the end of this procedure
the boiler can satisfy any kind of CH requests.
PUMP CYCLE MODE:
wen power is restored to the
PCB and/or the PCB is powered for the fi rst time, the
appliance will enter a 2-minute purge cycle whereby only
the pump will run for 15-seconds then off for 15-seconds
and will not “fi re” until this period has elapsed.
7.2.3 HEATING MODE
With the selector switch in the ON position and any
additional controls (time clock, programmer, room ther-
mostat, etc,) calling for heat, the appliance will operate
in the heating mode. The external pump and fan will be
activated via the fl ow 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 fl ame stability at the burner.
Once successful ignition has been achieved, the electro-
nic circuitry increases the gas rate to 75% of the MAX
Heating (set by the corresponding HTG trimmer) for a
period of 15 minutes. The speed of the fan and therefore
the output of the boiler is determined by the temperature
of the water sensed by the fl ow temperature sensor, con-
sequently a high temperature at the fl ow sensor results in
a lower fan speed. As the water temperature increases,
the temperature sensors – located on the fl ow pipe of the
boiler – reduce the fan speed via the electronic circuitry.
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 incre-
ase 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 5-minutes. When the
temperature of the fl ow 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 meas-
ured 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 2°C (hysterisis), the burner will shut down. A
new ignition sequence will be enabled when the 5- min-
ute anti-cycle has been performed and the temperature
at the primary thermistor has dropped 8°C (hysterisis)
below the set-point.
NOTES
When the request for heating and/or hot water has been
satisfi ed, 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
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