Technical data

Fig. 302:Functional sequence (heaters with control unit 1572D)
A
C
D
E
F
G
12 141412
13 15 13 15
1
2
6
8
2
9
6
10
3
5
3
7
1s 12s12s1s12s
max.
1s12s30s1s
max.
16
max.
120s
max.
max.
30s
16
max.
120s
A H1 Operating indicator light
C M2 Circulation pump
D U1 Igniter box
E M1 Combustion air fan
F Y1 Solenoid valve
G B1 Flame sensor
1 Switch on
2 Start
3 Flame-up, combustion operation
5 Temperature sensor – upper switching
threshold
6 Flame sensor – dark
7 Control idle
8 Temperature sensor – lower switching
threshold
9 Switch off
10 Heater – off
12 Start-up
13 Foreign light check
14 Pre-ignition
15 Safety period
16 Run-down
Thermo 230 / 231 / 300 / 301 / 350 3 Functional Description
305
3.8 Switch-off upon Failure (heaters with
control unit 1572D)
The heater switches off automatically when detecting one
of the following malfunctions.
Several subsequent switch-offs due to a malfunction will
cause the heater to enter an error lockout condition.
Flash pulses are output via the operating indicator light.
The combustion air fan and the circulation pump are
switched off after approx. 120 seconds.
Malfunctions during switch-on:
Short or open circuit of
– temperature sensor
– flame sensor
– burner motor
– solenoid valve
– igniter box
Malfunctions during start-up:
– short circuit of igniter box
– open circuit of igniter box
– flame detected by photo control circuit prior to high
voltage igniter spark.
– no flame detected after approximately 25 seconds
after heater start.
– short/open circuit or dry run (if programmed) of
circulation pump.
When using the circulation pump U 4851 approxi-
mately 15 seconds after switch-on the circulation
pump is automatically stopped and may only be
reactivated after approximately 2 minutes should
coolant be missing or the pump wheel be seized.
Malfunctions during heating operation:
– low voltage threshold of approximately 21V violated
for a duration of 20 seconds.
– no combustion for more than 10 seconds.
– temperature sensor short or open circuit.
– flame sensor short or open circuit.
– solenoid valve short or open circuit.
Malfunctions during heating operation:
(valid for application Thermo 350.190)
– low voltage threshold of approximately 18,5V violated
for a duration of 20 seconds.
– no combustion for more than 10 seconds.
– temperature sensor short or open circuit.
– flame sensor short or open circuit.
– solenoid valve short or open circuit.