Bosch Appliances 250SX LP, 250SX NG manual chapter, By installer or service technician only

Troubleshooting

Display	Cause	Solution
E9	Temperature limiter opened circuit (overheat).	Check connections.*
	Trips at 220F (104C).	Check heat exchanger condition.*
EA	No ionization during safety time (safety time out).	Check gas pressure.*
	Note: appliance makes 3 ignition attempts	Check that gas is not diluted with air, as a result
	before entering error mode “EA”.	from recent gas pipeline rework.*.
		Check if vent terminal is blocked (especially when
		the appliance starts up for some seconds and then
EC	The ionization signal momentarily disappeared
		looses ionization signal).*
	more then 5 times in less then 30 seconds.	Check ionization electrode.*
		Check for a proper ground.*
FA	Leakage error (gas valves do not close gas	Check gas valve and control unit.*
	circuit).
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	Check water temperature sensor/receiver and
	(from control unit).	connections.*
		Check room area temperature where heater is
		located, it must be above 36°F (2°C)
A9	Hot water temperature sensor/receiver mis-	Close water tap and allow 30 seconds for purging
	assembled (from control unit).	time.
	Note: if display shows “A9” flashing, the	Open water tap and wait for 2 minutes to see if A9
	appliance can be operated normally, but	message is deleted from the display.
	performance may be affected.	Check that the water temperature sensor/receiver is
		properly assembled in the water pipe.*
		Check that the water temperature sensor/receiver is
		in proper condition.*
C1	FAN rotation too low at start-up (from control	Check supply voltage.*
	unit).	Check fan and connections.*
		Check control unit.*
		Check if vent terminal is blocked or if vent terminal is
		according with chapter 2.9. *
		Check CO2 levels (see chapter 9).*
C6	FAN rotation too low at operation (from control	Check supply voltage.*
	unit).	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 CO2 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.

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