Flame discontinued or flame monitor defective during heater operation, function

P83.70-0396-09

1 Burner housing

2 Heat exchanger

3 Heater circuit thermostat

A6m1 Circulation pump

Y23 Fuel metering pump

B Thermostat setting, auxiliary circuit open

A6m2 Combustion air blower

A6n1 Stationary heater/heater booster control module

A6r2 Glow pin

N34 Stationary heater timer

Function sequence

1 Coolant temperature > 59 °C:
The thermostat (3) is set to the heating mode, the stationary heater auxiliary circuit is connected to the cooling and heating circuit of the vehicle.

2 The heater operates in the partial load or full load mode, the coolant circulation pump (A6m1) pumps coolant through the heat exchanger (2). The combustion air blower (A6m2) and fuel metering pump (Y23) operate at partial load or full load capacity or speed.

3 The glow pin (A6r2) acts as a flame monitor and continuously monitors the combustion in the burner
housing (1).

4 The glow pin signals:

 "cold" = flame terminated due to lack of fuel or combustion air.

 "cold" = glow pin defective.

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5 The control module (A6n1) attempts to restart the heater for approx. 85 s to reignite the flame and continue the combustion.

6 The fuel metering pump (Y23) and the combustion air blower (A6m2) pump run at their lowest capacity and speed.

7 The glow pin (A6r2) is switched on and resumes its actual function.

8.1 After expiration of the 85 s start-up attempt the glow pin is switched off and acts as a flame monitor signaling:

 "hot" = flame present and therefore combustion continued.

 The output or speed of the fuel metering pump and combustion air blower is matched to the heat requirement.

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8.2 After expiration of the 85 s startup attempt the glow pin is switched off and acts as a flame monitor signaling:

 "cold" = no flame present and therefore combustion not continued.

 Control module (A6n1) goes to malfunction shutoff.

 The fuel metering pump is switched off immediately.

 The heater malfunction shutoff delay for cooling the heater and purging the combustion chamber starts fpr approx. 110 s.

 The heater shutoff delay terminates. The combustion air blower (A6m2) and the coolant circulation pump (A6m1) switch off.

 To restart following a malfunction shutoff it is necessary to switch the heater off and back on after eliminating the cause of the malfunction.