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Safety devices

Safety devices

The heater flame is monitored by a flame temperature sensor and the maximum permissible temperature by coolant temperature sensor 2. Both these functions are checked by the control module, which disconnects the heater in the event of a malfunction.


1. If the heater fails to ignite within 90 seconds of the fuel supply being turned on, the starting sequence is repeated. Should the heater fail to ignite after another 90 seconds, or if it starts but then stops again, it will be disconnected because of a malfunction.

2. If the flame goes out by itself while the heater is in operation, a fresh starting sequence will be initiated.

If the heater fails to ignite within 90 seconds of the fuel supply being turned on, or if it ignites but then goes out again, it will be disconnected because of a malfunction.

If the heater has been disconnected because of a malfunction, such disconnection can be cancelled by switching it off and then on again.

3. In the event of overheating (low coolant level, cooling system not properly bled, circulation disturbances), coolant temperature sensor 2 sends a signal to the control module and the fuel supply will be cut off. The heater will then be disconnected because of a malfunction.

When the cause of overheating has been dealt with, the heater can be restarted by switching it off and on again (provided that it has cooled down sufficiently).

4. Should the power supply drop below about 10 V or exceed about 16 V, the heater will be disconnected (the undervoltage or overvoltage cut-out trips).

5. The heater will not start if the glow plug is defective or it there is an open circuit in the wiring to the fuel pump.

6. The combustion air fan is monitored continuously. If a fault is detected and it does not start or is blocked, a malfunction disconnection will be initiated automatically.