Bosch 250 SXO NG - Manual (Page 21)

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Troubleshooting
21
Display Cause Solution
E9 Temperature limiter opened circuit (overheat).
Trips at 220F (104C). Check connections. *
Check heat exchanger condition.*
EA No ionization during safety time (safety time out).
Note: appliance makes 3 ignition attempts
before entering error mode “EA”. Check gas pressure. (see chapter 2.9 ) *
Check that gas is not diluted with air, as a
result from recent gas pipeline rework.*.
Check if vent terminal is blocked (especially
when the appliance starts up for some sec-
onds and then looses ionization signal).*
Check ionization electrode.*
Check for a proper ground.*
Check CO
2
levels.* (see chapter 9)
EC The ionization signal momentarily disappeared
more then 5 times in less then 30 seconds. CO
2
may be out of adjustment
FA Leakage error (gas valves do not close gas
circuit). Check gas valve and control unit.*
F7 Ionization error (flame sensing at stand-by). Check control unit.*
E0 Internal software/hardware failure. Check control unit.*
A7 Hot water temperature sensor/receiver defect
(from control unit). Check water temperature sensor/receiver and
connections.*
Check incoming water temperature to heater, it
must be above 32°F (0°C)
A9
(flashing) Hot water temperature sensor/receiver mis-
assembled (from control unit).
Note: if display shows “A9” flashing, the
appliance can be operated normally, but
performance may be affected. Check that the water temperature sensor/receiver is
properly assembled on the horizontal of the hot
water pipe.*
Check that the water temperature sensor/receiver is
free from corrosion or moisture.*
C1 FAN rotation too low at start-up (from control
unit). Check supply voltage.*
Check fan and connections.*
Check control unit.*
Check if vent terminal is blocked.*
C6 FAN rotation too low at operation (from control
unit). Check supply voltage.*
Check fan and connections.*
Check control unit.*
C7 No rotational speed sensor signal from FAN Check fan and connections.*
Check control unit.*
CA Water flow signal over specified maximum value Check water valve and flow sensor.*
E2 Inlet temperature sensor fault Check water temperature sensor/receiver and
connections.*
Check incoming water temperature to heater, it
must be above 32°F (0°C)
A2 Overheat protection fault Check connections to the overheat protection.*
Check sensor continuity.*
Check heat exchanger sealings and walls.*
Table 5
* By installer or service technician only.