Bosch C 950 Installation Manual page 52

52 | Problem solving
Display Cause
E9 Overheat sensor (ECO) open circuit
(resets when cooler temperatures are
detected 220°F/104 °C).
EA No flame ionization detected with
water flow.
EC Ionization failure during operation.
Table 54
* By installer or service technician only.
6 720 805 440 (2014/11)
Solution
1. Disconnect power supply cord and check wire connections on the overheat sensor (fig.
80, page 57) and the two connectors on the control board.
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. In areas where water has a high mineral content, periodic descaling may necessary, see
chapter 7.3, page 42.
5. 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.
1. Verify that all manual gas shut off valves are open.
2. Check gas type. See fig. 2, page 8.
3. Reset error code and open a water tap to cycle the heater in an effort to purge air. Cycling
hot water tap on and off multiple times may be necessary. If heater still faults with EA error
code, have a licensed gas technician properly purge air out of the gas line leading to the
water heater.
4. Check three wire connections on the lower front of the heat exchanger are secure.
5. Check gas pressure. See chapter 4.14, page 36.
6. Check venting specifications are met. Improper venting may cause premature failure of
the flame sensor rod. See chapter 4.3, page 11.
7. Check that the minimum power fan speed has been adjusted to the proper value. See
page 22.
8. Observe inside the viewing window of the heat exchanger when a hot water tap is
opened. Sparking should be followed by a steady blue flame. If flame is unstable/yellow with
proper gas pressure, confirm CO
1. Check gas type, fig. 2, page 8.
2. Check three wire connections to ignition group on the lower front of the heat exchanger
are secure.
3. Verify that venting specifications are met. Improper venting may cause premature failure
of the flame sensor rod. See chapter 4.3, page 11.
4. Check gas pressure. See chapter 4.14, page 36.
5. Check and adjust CO2 readings. See chapter 7.5, page 43.
6. Check that the minimum power fan speed has been adjusted to the proper value. See
page 22.
readings per chapter 7.5, page 43.
2
Greentherm