4 Heater functions Thermo E 200 / 320
404
4.3 Malfunction interlock and heater
interlock
Malfunction interlocks and heater interlocks are distin-
guished.
The interlocks protect the heater and the surrounding
vehicle assemblies against sequence errors after failure
of individual heater components and particularly against
impermissible thermal loads.
Thermal loads can be triggered by:
• Coolant flow too low
• Coolant circuit not or only partially filled (dry over-
heating)
• Circulating pump failure.
The control unit software detects overheating. Over-
heating is also detected by hardware (overheating protec-
tion), independently from software.
4.4 Malfunction interlock
If one of the malfunctions listed below occurs, the heater
will initiate a fault shut-down, followed by malfunction
interlock.
Depending on the error time, a purge cycle up to 120
seconds duration can be executed.
An error code is outputted by means of flash impulses via
the operating display.
In case of several sequential malfunction interlocks a
heater interlock is initiated (see 4.6).
4.4.1 Malfunctions during switching-on and
start procedure
NOTE
If malfunctions occur during switching-on or during the
start process prior to ignition, the heater will be switched
off without purge cycle.
The heater is in malfunction interlock.The motor stops
immediately or does not start.
Malfunction criteria:
• Short circuit and/or interruption of electrical compo-
nents:
– Burner motor (stops immediately)
– Electronic ignition unit
– Optional nozzle block preheater
• Interruption of circulating pump operation
• Flame or extraneous light detection by the flame
detector prior to ignition of the high-voltage ignition
spark.
• No start: No flame detection within 15 seconds after
opening the solenoid valve.
• Temperature sensor delivers unacceptable tempera-
ture values.
• Heater operation outside the permissible temperature
range.
• Voltage falling short of the low voltage threshold of
approx. 20.5 V at motor start or within a duration of 20
seconds after a heating request.
• Voltage exceeding the high voltage threshold of
approx. 30 V at motor start or within a duration of 6
seconds (purge cycle only, no malfunction interlock).
4.4.2 Malfunctions during heater operation
NOTE
In case of malfunctions during heater operation, first a 120
seconds purge cycle will be performed. Then the heater is
switched into the malfunction interlock.
Malfunction criteria:
• Short circuit of the circulating pump.
• Short circuit or interruption of other electrical compo-
nents (motor, solenoid valve, electronic ignition unit,
nozzle block preheater).
• Water temperature greater than the upper switching
threshold.
• Temperature sensor delivers unacceptable tempera-
ture values.
• Heater operation outside the permissible temperature
range.
• Flame interruption (combustion interruption for longer
than 15 seconds).
• Voltage falling short of the low voltage threshold of
approx. 20.5 V at motor start or within a duration of 20
seconds after a heating request.
• Voltage exceeding the high voltage threshold of
approx. 30 V at motor start or within a duration of 6
seconds (purge cycle is applied, but no malfunction
interlock).
• Control unit malfunction.
4.4.3 Malfunctions during purge cycle
Malfunction causes:
• Short circuit or interruption of the burner motor (stops
immediately)
• Interruption of circulating pump operation
• Heater operation outside the permissible temperature
range.
• Voltage falling short of the low voltage threshold of
approx. 20.5 V at motor start or within a duration of 20
seconds after a heating request.
• Voltage exceeding the high voltage threshold of
approx. 30 V at motor start or within a duration of 6
seconds (purge cycle is applied, but no malfunction
interlock).
• Control unit malfunction.
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