19
2.13
ELECTRONIC BOARD
The electronic boards of the
“MURELLE - MURELLE
BF”
boilers are manufactured in compliance with the
EEC 72/23 low-voltage directives. They are supplied with
230 V and, through a built-in transformer, send a voltage
of 24 V to the following components: modulator, water
pressure switch, smoke pressure switch and thermostat,
D.H.W. and C.H. sensors, room temperature thermostat,
“Summer/Winter” switch, and limit thermostat. An auto-
matic and continuous modulation system enables the
boiler to adjust the heat output to the various system
requirements or the User’s needs. The electronic compo-
nents are guaranteed to function in a temperature range
of -10°C to +60°C.
2.13.1 Central heating operation
Upon demand for heating from the room temperature
thermostat, the circulation pump is activated, and
approximately 120 seconds must elapse for the burner to
start operating. This will happen only if the temperature is
set above the value detected by the heating sensor.
The setting range is between 35°C and 80°C. The heat
output can be varied according to the system needs by
adjusting the trimmer located between the two potentio-
meters (Section 3.4).
At start-up of each working cycle, after the period of slow
ignition having a duration of approx. 8 sec, the boiler will
set itself, for 60 sec, at the heat output set on the
‘Minimum heating pressure’ trimmer. Then it will switch to
the output set.
At the end of the heating phase, the post-circulation
pump will be activated. This lasts 20 sec. and limits the
possibility of thermal inertia and recovers the residual
calories still present in the primary exchanger.
2.13.2 D.H.W. operation
Upon demand for hot water, the boiler starts instanta-
neously when the microswitch on the pressure switch
valve trips. The required power output is regulated, via
flame modulation, by the hot water sensor, which will
compare the temperature read with the temperature set
on the potentiometer.
The adjustment range is between 35°C and 60°C.
Two limits are set for switching off the boiler:
– when the temperature exceeds 65°C on the D.H.W.;
– when the temperature exceeds 85°C on the heating
flow sensor.
In the first case the boiler will be turned back on when the
D.H.W. temperature has dropped below 60°C; in the
second case, when the heating flow sensor is at 75°C.
2.13.3 Check-Control
The electronic board is equipped with control leds which
show some of the possible failures that can cause an irre-
gular and/or improper operation of the appliance.
The leds are arranged on the card as indicated in Fig. 25
and marked with the following wording:
–
SMOKES:
red LED lit up because the fume safety
thermostat or the fume pressure switch (
“MURELLE
20 TX CE IONO - MURELLE BF”
versions) have
tripped.
–
REQUEST FOR IGNITION
: green LED lit up on
demand for D.H.W. or heating.
–
LINE
: green LED lit up when electric power is rea-
ching the electronic board.
–
SENSORS INTERRUPTED:
red LED lit up because
the SM sensor (heating flow sensor) is interrupted; in
this case, the boiler operates always at minimum
power output in heating.
KEY
1 Fuse (T100 mA)
2 Fuse (T1,6 A)
3 “Request for ignit” led
4 “Smoke” led
5 “Sensors interrrupted” led
6 “Heating output” trimmer
7 “Ignition pressure” trimmer
8 “Minimum pressure” trimmer
9 “Cancel delays” bridge
10 “MET - L.P.G.” bridge
11 “Line” led
Fig. 25
