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Bosch Error Codes & Diagnostic Codes

Updated · by Aurora Star Tech Inc.

Bosch error codes and diagnostic codes: look up a code to see what it means, the likely causes and the steps to fix it.

Bosch error codes by equipment type

Bosch Air Handler error codes

CodeMeaning
2 flashesIndoor T2 sensor fault
3 flashesRefrigerant sensor fault
4 flashesRefrigerant sensor communication fault
5 flashesIndoor-to-outdoor communication fault
8 flashesRefrigerant sensor past service life
Continuous flashingR-454B refrigerant leak protection
LED offPower supply failure

Bosch Boiler error codes

CodeMeaning
A7DHW temperature sensor fault
A8Communication fault
AdDHW tank temperature not detected
b1Code plug not detected
b2/b3/b4/b5/b6Internal data error
b7Burner control fault
C6Fan not running
CCOutdoor temperature sensor not recognised
d3High limit / temperature limiter circuit open
d5External supply temperature sensor fault (low-loss header)
E2Supply temperature sensor fault
E3Additional supply temperature sensor fault
E9Safety high limit or flue gas limiter tripped
EANo flame detected
F0Internal fault
F1Internal data error
F7Flame detected with burner off
FAFlame detected after gas shut off
FdReset button pressed by mistake

Bosch Heat Pump error codes

CodeMeaning
AtLAmbient temperature limited
b2Indoor T2 sensor fault
b3Indoor refrigerant sensor hardware fault
b4Indoor refrigerant sensor communication fault
b5Indoor to outdoor communication fault
b7R-454B refrigerant leak protection
b8Refrigerant sensor past service life
C3T3 coil sensor not reading correctly in cooling
E7T5 discharge sensor not reading correctly
E41T3 temperature sensor fault
E42T3L temperature sensor fault
E43T4 temperature sensor fault
E44T5 temperature sensor fault
E45Th temperature sensor fault
E51Input voltage out of range
E52DC bus voltage out of range
E81EEV coil fault
EAControl and drive program mismatch
F1High pressure switch protection
F2System lockout (5 low-pressure trips in 100 minutes)
F4Pressure transducer fault
F41High pressure sensor fault
F42Low pressure sensor fault
H01Drive chip communication fault
J00-JCFCompressor driver fault
n00-nCFOutdoor fan motor driver fault
o37Low refrigerant in heating
P0Control board / compressor IPM overheating
P1High pressure protection
P4High compressor discharge temperature
P5Condenser coil temperature protection (cooling)
P11High pressure protection (transducer)
P21Low pressure protection
P31Input over-current protection
P32Compressor over-current protection
PHLow discharge superheat protection

Bosch Tankless Water Heater error codes

CodeMeaning
A0Water temperature sensors disconnected or damaged
A1Cabinet air temperature above 158 F (70 C)
A2External water temperature sensor / aquastat fault
A3Flue gas temperature sensor fault
A4Air temperature sensor fault
A5Condensing unit flue temperature sensor fault
A6Inlet cold water temperature sensor fault
A7Heat exchanger hot water temperature sensor fault
A8Outlet hot water temperature sensor fault
A9Output power too low
AAFlue gas temperature too high, power limited
ADPower derate warning
BBFan calibration after missed ignitions
BCRepeated fan calibration with similar values
C1Flue blockage at start-up
C2Flue blockage at start-up
C3Flow sensor sees no recirculation
C5Bypass water valve fault
C7Fan fault
C8Main water valve fault
C9Barometric pressure sensor damaged
CAWater flow above 9.2 gpm
CEFlue blockage during operation (siphon pressure)
CFFlue blockage during operation (insufficient air)
E0Control unit internal error
E1Hot water above 194 F (90 C)
E3Flue gas temperature too high, burner cut off
E4Cabinet air too hot, burner cut off
E5Condensing unit flue too hot, burner cut off
E7Control unit internal error
E8Ionization test error
E9Thermal fuse open
EAIgnition failure
EBControl unit internal error
ECFlame lost during operation
EEGas valve modulation coil disconnected
EFWrong gas type configured
F2Control unit internal error
F3Control unit internal error / configuration
F7Control unit internal error
F8Control unit internal error
F9Gas valve driver fault
FAGas leak in the gas path
FCTouch key held over 20 seconds

Find codes by Bosch model

Bosch IDS Plus/Premium air handler

BIVA20-24BIVA20-36BIVA20-48BIVA20-60

Bosch IDS Light

BOVA15-24BOVA15-36BOVA15-60

Bosch IDS Premium Connected

BOVA36-20BOVA60-20

Bosch Greentherm T9800 SE

Greentherm T9800 SE 160Greentherm T9800 SE 199Greentherm T9800 SEC 199

Bosch Greentherm T9900 SE

Greentherm T9900 i 199Greentherm T9900 SE 160Greentherm T9900 SE 199

Bosch Greenstar

ZBR21-3AZBR28-3AZBR35-3AZBR42-3A

General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.

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