Bosch Therm 8000 S Installation And Operating Instructions Manual page 43

Display Cause
Hot water temperature sensor
(NTC) at the exit of the
appliance detect a high
temperature of the hot water.
Temperature > 85°C
Cold water temperature sensor
fault.
Exhaust temperature sensor -
the appliance will close the
burner and lock if it gets over
90°C. (only applied for
condensing unit)
Backflow temperature sensor
over 130 °C.
The appliance will close the
burner and lock (non-volatile).
Overheat sensor (ECO) open
circuit (resets when cooler
temperatures are detected
104 °C).
Table 25
* By installer or service technician only.
Therm 8000S
Solution
1. Check the correct position and fixation of the NTC sensor.
2. Check the electric connections and connectors of the hot water
temperature sensor. Clean terminals. If the terminals are rusted,
replace the sensor and cables. Check resistance (see Fig. 3, [2]).
3. Clean the water filter, any dirty in the faucets and also all the water
filters of the installation.
4. In areas where water has a high mineral content, periodic descaling
may necessary.
1. Check connector on wires coming from top of watervalve for a secure
connection.
2. Sensor may trip if water temperature drops below 2°C. Protect
heater from freezing conditions as any damage due to freezing
conditions is not covered under warranty.
3. Check sensor.
1. Clean and check heat exchanger.
2. Clean and check condensing heat exchanger.
3. Reduce maximum power.
4. Reduce water temperature.
1. Check inlet/outlet vent pipes.
2. Check if secondary fan connections are disconnected.
3. Check if venting specifications are met. Long vent lengths, venting
with more than three elbows, blocked vent or combination venting may
cause this failure.
4. Call the Technical Assistance.
1. Disconnect power supply cord and check wire connections on the
overheat sensor and the two connectors on the control board. see
Fig. 2, [7].
2. Check white wire connections at the overheat sensor. Clean terminals
with an eraser. If badly corroded, replace sensor and wire harness.
3. Check that venting specifications are met. Long vent lengths, venting
with more than three elbows, blocked vent or combination venting may
cause this failure.
4. Clean the water filter, any dirty in the faucets and also all the water
filters of the installation.
5. In areas where water has a high mineral content, periodic descaling
may necessary.
6. Unplug power supply cord to the water heater. Open a hot water tap
for several minutes to allow cold water to pass through heat exchanger.
Close hot water tap and disconnect lead wires to overheat sensor. Using
a multimeter, check continuity through overheat sensor contacts.
Replace sensor if open.
Problem solving | 43
6 720 680 174 (2014/05)