Flame-Out/Flame Monitor Malfunction During Heater Operation

Flame-out/Flame Monitor Malfunction During Heater Operation, Function

Shown On Models 215, 220:

Operating procedure
1 Coolant temperature > 65 degrees C and < 77 degrees C
2 Depending on heat requirements, the STH heater or heater booster operates in partial-load or full-load mode:
- The STH or heater booster fuel metering pump (Y23) and the combustion air blower (A6m2) deliver at their minimum or maximum speeds and outputs.
- The coolant circulation pump (A6m1) delivers the coolant via the heat exchanger (2) and the heating and cooling circuits.
- The vehicle blower feeds pre-heated air into the interior.

3 In its function as flame monitor, the flame monitor heater element unit (A6r4) continuously monitors combustion in the burner housing (1).
4 The flame monitor glow pin unit (A6r4) signals:
"cold" = flame-out because of lack of or inadequate fuel or combustion air supply
or
"cold" = glow pin malfunction in flame monitor glow pin unit (A6r4).

5 The STH or heater booster control module (A6n1) initiates a start attempt for approx. 85 s to light a new flame and start the combustion process:
- The STH or heater booster fuel metering pump (Y23) and the combustion air blower (A6m2) deliver at their minimum speeds and outputs.
- The heater element of the flame monitor heater element unit (A6r4) is switched on and resumes its function.

6.1 After the start attempt, which lasts for approx. 85 seconds, the glow pin is switched off, the flame monitor glow pin unit (A6r4) signals in its function as flame monitor:
"hot" = flame present again - Combustion continues.
The STH or heater booster fuel metering pump (Y23) and the combustion air blower (A6m2) adjust their output and rotational speed to heat requirements again.

6.2 Following the expiry of the 85 s long attempt at starting, the heater element is switched off, the flame monitor heater element unit (A6r4) reports in its function as flame monitor:
"cold" = no flame formation
The STH or heater booster control module (A6n1) triggers a heater malfunction delayed switch-off with subsequent malfunction shutoff for approx. 120 s.

The STH or heater booster fuel metering pump (Y23) is switched off and the operating and control module (N18, N22 or N22/7) is actuated via the CAN class B (CAN-B) with the signal "Fan off".
- The control and operating module (N18, N22 or N22/7) switches the vehicle blower off and switches from stationary heating mode to normal operating mode.

The malfunction delayed switch-off has finished:
- The combustion air blower (A6m2) and the recirculation pump (A6m1) are switched off.
- The green or red indicator lamp in the STH switch (N72s12 or S46) is extinguished.
Malfunction shutoff is present.

NOTE: In order to restart, the STH heater or heater booster must be switched off and on again at the STH switch (N72s12 or S46) after the malfunction has been remedied.