Bosch Singular 4000 - Page 37

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Service Manual
Singular Combi Boiler - BTC 439002301 A (12.2021)
AC Error - Wire Check
1. Check the connection of the wire.
Figure 42 Control Board
Figure 43 DHW Sensor
AC Error - DHW Sensor Check
1. Measure the resistance of the DHW sensor. If the resistance is not normal,
replace the DHW sensor.
— Disconnection: OL
— Normal: 86 °F: 40 kΩ
140 °F: 12.4 kΩ
185 °F: 3.9 kΩ
Figure 44
KΩ
AC Error - Disconnection Check
1. Check if the sensor is disconnected.
— Disconnection: OL
— Normal: 86 °F: 40 kΩ
140 °F: 12.4 kΩ
185 °F: 3.9 kΩ
Figure 45
kΩ
AC Error - Short Circuit Check
1. Check if the DHW sensor has short-circuited.
— Short circuit: 0 Ω
— Normal: 86 °F: 40 kΩ
140 °F: 12.4 kΩ
185 °F: 3.9 kΩ
Figure 46
Ω
AC Error - Control Board Check
1. If the wire connection and the resistance of the DHW Thermistor are normal,
replace the control board.