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Internal diagram
LGA41...
Legend
8/11
Siemens Building Technologies
HVAC Products
When the switch-on command is given, power is supplied to the ignition transformer
and the heating coil of the bimetal sequencing device.
The bimetal bends and pushes contact set «c, d, e» towards «f».
On completion of the preignition time, the system tilts so that «e - f» closes and «f - g»
opens, «BV1» receives voltage.
Contacts «c - d» still remain closed («c» resting on «d»).
On flame establishment, the flame relay is energized, latching mechanically «e - f» in
the position now assumed.
The relay also closes contact «f» and, at the same time, opens «c - d», so that the igni-
tion transformer and the bimetal heating element will be switched off.
Then, «d» slowly returns to its starting position, also catching «g».
When tilting back, «g - f» closes, so that the main gas valve «BV2» will be energized.
If no flame signal is generated, the flame relay does not open «c - d», so that the bi-
metal will continue to be heated.
The bimetal thus continues to bend until – tilting – it actuates contact «tz2»: → Lockout.
In the event of an erroneous premature flame signal, the flame relay – by means of its
latch – prevents «e - f» from making, which means no release of gas.
«TZ», however, still receives power so that the bimetal continues to bend until, eventu-
ally, lockout is initiated by «tz2».
tz2
L1
EK
X Y Z
1
2
10
9
SB
W
AL
R
Si
H
L
N
AL
Fault status signal
BV...
Fuel valve
EK
Lockout reset button
ION
Ionization probe
FR
Flame relay
L1
Built-in lockout warning lamp
H
Main switch
tz1
a b
c d
f g
e
fr
TZ
8
3
7 6
4
11
Z
BV1
R
SB
Si
TZ
W
Z
LGA41...
FR
12
5
ION
BV2
7418i02/0304
Thermostat or pressurestat
Safety limit thermostat
External primary fuse
Electro-thermal timer
(bimetal system) with contacts «tz»
Limit thermostat
Ignition transformer
CC1N7418en
08.04.2004
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