Bosch Singular 4000 - Page 35

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Service Manual
Singular Combi Boiler - BTC 439002301 A (12.2021)
AB Error - Wire Check
1. Check the connection of the wire.
Figure 35 Control Board
Figure 36 Heating Water Sensor
AB Error - Heating Water Sensor Check
1. If the resistance is not normal, replace the Heating water sensor.
— Disconnection: OL
— Normal: 86 °F: 40 kΩ
140 °F: 12.4 kΩ
185 °F: 3.9 kΩ
Figure 37
KΩ
AB Error - Disconnection Check
1. Check if the heat exchanger overheat sensor is disconnected.
— Disconnection: OL
— Normal: 86 °F: 40 kΩ
140 °F: 12.4 kΩ
185 °F: 3.9 kΩ
Figure 38
kΩ
AB Error - Short Circuit Check
1. Check if the Heating water sensor has short-circuited.
— Short circuit: 0 Ω
— Normal: 86 °F: 40 kΩ
140 °F: 12.4 kΩ
185 °F: 3.9 kΩ
Figure 39
Ω
AB Error - Control Board Check
1. If the wire connection and the resistance of the heat exchanger overheat
sensor are normal, replace the control board.