Bosch WTD 12-4 AME 23 - Overview of ECU (Electronic Control Unit) MPP

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Part Name
Wire color
Value
Remarks
Water flow
sensor
Red-Black GND
5 VDC
Input Power from PCB
Yellow-Black GND
≈ 2.4 VDC
Pulse
frequency Hz
Start-up: ≥ 2.8l/min
Shut-off: ≤ 2.4/min
Check the water flow character
formula above, and calculate the
frequency correspondent to different
water flow.
Thermal fuse
(activation
temperature:
192°C)
Bimetallic
thermostat
(activation
temperature):
85ºC
Use the multi-meter to test the resistance
R（Ω ）
White-White
Open circuit
Not OK
Close circuit = continuity
Ok
Air
temperature
sensor NTC
The R (Ω) – T (ºC) table is for
reference.
Outlet water
temperature
sensor NTC
The R (Ω) – T (ºC) table is for
reference.
Inlet water
temperature
sensor NTC
The R (Ω) – T (ºC) table is for
reference.
Flame sensor
Yellow wire
Use the multi-meter to test
the ion current,
which should be > 8 μA
The multimeter for current
should be in series between
the flame sensor and the ECU
wire.
DC fan
(variable
speed in MPP)
Red-black
GND
36V DC
Input Power
Yellow-black
GND
0~5V
PWM adjust speed
White-black
GND
DC-V pulse frequency Hz
Fan rotation rate feedback
(Rotation rate= frequency *15)
Gas valve
Red (+) /
Brown (-)
~0-12VDC
Current=0-140mA
Resistance：84Ω
MPP type gas valve
Polarity must match in the solenoid
Main valve
Yellow-black
Remain open the valve:
14 VDC
Close the valve:0VDC
Resistance：115Ω
MPP type safety valve