Bosch AQUA STAR 250SX LP - Manual (Page 26)

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Troubleshooting
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). Check gas pressure.*
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 seconds and then
looses ionization signal).*
Check ionization electrode.*
Check for a proper ground.*
EC The ionization signal momentarily
disappeared more then 3 times in less then
30 seconds.
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 room area temperature where heater is
located, it must be above 36°F (2°C)
A9 Hot water temperature sensor/receiver mis-
assembled (from control unit). Check that the water temperature sensor/receiver is
properly assembled in the water pipe.*
Check if vent terminal is blocked or if vent terminal is
according with
chapter 2.9 .*
In case of high altitude installation confirm that
necessary adjustment steps have been taken.*
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 or if vent terminal is
according with
chapter 2.9 . *
Check CO
2
levels (see chapter 9 ).*
C6 FAN rotation too low at operation (from
control unit). Check supply voltage.*
Check fan and connections.*
Check control unit.*
Check if vent terminal is according with
chapter 2.9 .*
C7 No rotational speed sensor signal from FAN Check fan and connections.*
Check control unit.*
Check CO
2
levels (see chapter 9 ).*
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 room area temperature where heater is
located, it must be above 36°F (2°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.