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24
UNICA BHE
SECTION 7 CHECKS, ADJUSTMENTS AND FAULT FINDING
7.1
CHECKING APPLIANCE OPERATION
When carrying out any repairs or servicing to the
appliance, the relevant commissioning procedure
must be undertaken to ensure the continued safe
operation of the appliance. Particular attention should
be made to ensure gas tightness, water tightness
and the electrical integrity of the appliance.
7.2
APPLIANCE MODES OF OPERATION
NOTE
There must be sufficient system water pressure
(min. 0.5 bar) to ensure the water pressure switch
is activated. If there is insufficient system pres-
sure the pump and fan will be prevented from
operating and the low-pressure fault code will be
displayed.
The 2-digit display can show several different
modes of operation:
Standby/OFF mode
Frost protection mode active
Combustion analysis mode active
Autostop function active
Normal heating request (example 60
o
C).
Normal DHW request (example 60
o
C).
7.2.1
SELECTOR SWITCH IN THE OFF/RESET PO-
SITION
When the selector switch is in the OFF/RESET
position, the following functions are active.
Active functions
:
•
frost-protection system
•
pump & fan anti-block
7.2.1
ON-BOARD FUNCTIONS
•
THERMOREGULATION:
when an external sen-
sor is connected to the appliance, the electronic
circuitry will automatically adjust the flow outlet
temperature to suit local weather conditions in
order to maintain comfort and efficiency. A
specific operating curve that is most suited to
the system type and geographical area can also
be selected.
•
OPE:
OT+ is a communication pro-
tocol that enables the boiler to be linked or
connected to other OT+ controls. These con-
trols have been designed to further increase fuel
economy by ensuring the boiler remains in the
modulation phase during any heating requests.
This reduces the amount of ON/OFF periods
and therefore increases fuel efficiency.
•
AUTOSTOP:
further information on the
AUTOSTOP function, can be obtained from
your local Vokera Sales Representative.
•
CO FUNCTION:
the CO function when acti-
vated, will allow the appliance to run at maxi-
mum 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 period, anti-
cycle, set-point, etc). Once enabled, the CO
function will remain active for a 15-minute pe-
riod, 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 6°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
30-seconds.
•
ANTI-CYCLE FUNCTION:
the anti-cycle func-
tion ensures the burner remains switched off for
at least 3-minutes after the set-point hysterisis
(set-point + 5-deg).
•
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.
•
ACTUATOR ANTI-BLOCK FUNCTION:
when
there has been no heating or HW request for 24-
hours, the anti-block cycle is activated. The
divertor valve actuator will motor briefly to the
heating position, and then back to the DHW
position.
•
DHW PRE-HEAT FUNCTION:
when the mode
selector switch is in the DHW pre-heat position,
the appliance will light periodically to maintain the
temperature of the DHW heat exchanger. When
the DHW thermistor and the primary thermistor fall
below 35
o
C and 55
o
C respectively, the boiler will
fire on m25% power until the primary
thermistor exceeds 55
o
C. Thereafter the pump
will over-run for a period of 30-seconds.
7.2.5
HEATING MODE
With the selector switch in the heating & hot water
position and any additional controls (time clock,
programmer, room thermostat, etc.) calling for
heat, the appliance will operate in the heating
mode. The pump and fan will be activated via the
flow temperature sensor. When the fan is sensed
to be operating correctly (tacho signal), the igni-
tion sequence commences. Ignition is sensed by
the electronic circuit to ensure flame stability at
the burner. Once successful ignition has been
achieved, the electronic circuitry increases the
gas rate to 75% 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 flow temperature sensor,
consequently a high temperature at the flow sen-
sor results in a lower fan speed. As the water tem-
perature increases, the temperature sensors –
located on the flow pipe of the boiler – reduce
the fan speed via the electronic circuitry. De-
