20
2.13.4 Devices present on the electronic board
The electronic board of the
“MURELLE”
boilers is equip-
ped with the following devices:
–
“IGNITION PRESSURE” trimmer
(7, Fig. 25):
The electronic board has an ‘IGNITION PRESSURE’
trimmer for varying the pressure level upon ignition
(STEP) of the gas valve.
According to the type of gas for which the boiler is
prepared, the trimmer must be regulated so as to
obtain a pressure of approx. 3.5 mbar at the burner for
methane gas and 7 mbar for L.P.G.
To increase pressure, turn the trimmer clockwise; to
reduce pressure, turn the trimmer counterclockwise.
Fig. 25/a gives an indication of where to set the trim-
mer according to the type of gas used.
–
“MINIMUM HEATING PRESSURE” trimmer
(8, Fig. 25/a):
This is the minimum point of modulation in heating to
maintain a pressure level higher than the one set for
hot water.
NOTE: After setting the pressure level upon igni-
tion (STEP) according to the type of gas, check
that the pressure for heating is still at the value
previously set.
–
“MET-L.P.G.” connector
(10, Fig. 25):
The connector link must be inserted on the type of gas
for which the boiler is prepared.
–
“CANCEL DELAYS”
connector (9, Fig. 25):
In the heating phase, the electronic board is program-
med to include a burner technical delay interval of
approx. 2 minutes, which occurs both at system cold
starting and at subsequent re-ignitions. The aim is to
overcome the problem of repeated ignition and turning
off with very short time intervals between. This could
occur in particular in systems presenting high head
losses. At each restart after the period of slow ignition,
the boiler will set itself for about 1 minute at the mini-
mum modulation pressure, and will then move to the
heating pressure value set.
When the connecting link is inserted, both the pro-
grammed technical pause and the period of operation
at minimum pressure in the startup phase will be can-
celled. In this case, the times elapsing between tur-
ning off and subsequent re-ignition will depend on a
temperature difference of 8°C detected by the SM
sensor (heating flow sensor).
NOTE: It is essential that the operations described
above be carried out by authorized technical staff;
otherwise, the warranty will be rendered null and
void.
2.14
TEMPERATURE SENSORS
The
“MURELLE”
boilers are equipped with sensors for
detecting temperature:
–
SM:
heating flow sensor, located on the outlet pipe of
the primary exchanger (10, Fig. 3 - 15, Fig. 3/a).
–
SS:
D.H.W. sensor (except for
“20 R CE IONO - 2
BFR CE IONO”
versions), located on the D.H.W. outlet
pipe (2, Fig. 3 - 2, Fig. 3/a).
The sensors are of the NTC type mod. ST03 and are
interchangeable.
Table 7 shows the resistance values
that are obtained on the sensors as the temperature
varies.
NOTE: With the SM heating flow sensor interrupted,
the boiler operates in the heating phase always at the
minimum heat output, whereas it works normally
when generating hot water. If this occurs on the SS
hot water sensor, the boiler works always at nominal
load and loses flame modulation.
2.15
ELECTRONIC IGNITION
The
“IONO”
version boilers are provided with automatic
ignition (without pilot burner).
They are therefore equipped with FM11 electronic control
and protection.
Ignition and flame detection is controlled by two electro-
des located on the burner.
These guarantee maximum safety with intervention times,
for accidental switching off or gas failure, of within one
second.
METANO
MAX. - G.P.L.
MIN.
Temperature
Resistance
C°
Ω
20
12.000
30
8.300
35
6.900
40
5.800
45
4.900
50
4.100
55
3.500
60
3.000
70
2.200
80
1.700
TABLE 7
METHANE
MIN.
MAX. - L.P.G.
Fig. 25/a
