Bosch Junkers error codes — full list with meanings | TroubleAtlas

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HVAC Error Codes · Manufacturer index

Bosch Junkers error codes

The complete list of Bosch Junkers fault codes shown on the display, each with what it means and the page that explains how it is diagnosed and fixed.

66documented codes
66with documented causes
Bosch Junkers boiler with the fault code shown on the display
Quick Answer

Bosch Junkers heating appliances display 66 documented error codes. Each code below opens its own page with the official meaning, the documented causes, the safety assessment and the parts involved.

01

All Bosch Junkers Error Codes

66 codes, each with its own page. Click a code to open the meaning, the documented causes and the repair.

CodeWhat it means
1017Water pressure too low
1021Domestic hot water temperature sensor on the plate heat exchanger defective
1022Kettle temperature sensor: contact problem or defective
1065Pressure sensor defective or not connected
1073Flow temperature sensor short circuit
1074No signal present from the flow temperature sensor
1075Temperature sensor short circuit on the primary exchanger
202The appliance is in the switching optimization program the time interval for re-ignition of the burner has…
2052The maximum activation duration of the ignition transformer has been exceeded
208The appliance is in chimney-sweep (flue test) mode After 30 minutes the chimney-sweep (flue test) mode is…
212Safety sensor temperature increase or heating flow temperature sensor too fast
214During the safety time the fan is turned off
215Fan too fast
227No flame signal after ignition
228Flame presence signal already before the burner is ignited
229Flame off during burner operation
234Gas valve electrical malfunction
281Heating circulation pump blocked or air in the heating circulation pump
2912No flame presence signal during calibration
2913Flame presence signal too low during calibration
2917No flame presence signal during combustion adjustment control
2920Flame control malfunction
2927The flame is not recognized during ignition
2942No speed message from fan
2943Mains voltage too low
2944Air pressure switch open
2947The anti-blocking protection of the circulation pump is active
2948No low power flame presence signal
2949No high power flame presence signal
2950No flame presence signal after the start-up phase
2951Flame failure - too many flame losses during a heat request
2953No low power flame presence signal
2954No high power flame presence signal
2961No signal present from the fan
2963The signal coming from the primary exchanger temperature limiter and the flow temperature sensor is outside…
2966Too rapid temperature increase of the heating flow temperature sensor and the temperature sensor on the…
2967Excessive temperature difference between the flow temperature sensor and the primary exchanger temperature…
2971Operating pressure too low
2972Mains voltage too low
306Flame presence signal after closing the fuel supply
323Command communication malfunction
350Flow temperature sensor short circuit
351Heating flow temperature sensor interruption
356Insufficient heat generator supply voltage
363Malfunction of the device's electronic system: error during the ionization signal test
815Defective hydraulic compensator temperature sensor
A1Low pressure or lack of water in the system, the modulating circulation pump ran dry
A3Flue gas temperature sensor not recognised
A4Leakage of burnt gases near the draft breaker, detected by the burnt gas control sensor
A6Temperature sensor in the combustion chamber not recognized
A7The DHW NTC sensor is interrupted or short-circuited
A9Hot water temperature sensor mounted incorrectly
C1The fan speed is too low
C4The burner and fan have been running continuously for 24 hours and are switched off briefly for an automatic…
C6Fan too fast
C7During the safety time the fan is turned off
E2Defective flow temperature sensor (short circuit)
E5The burner flow sensor has exceeded the temperature
E7Temp
E9Intervention of the primary exchanger temperature limiter or of the flue gas temperature limiter
F0Defective gas valve connection cable, gas valve or control panel
H12Defective boiler temperature sensor
H15Defective return temperature sensor
H16Temperature sensor signals too different
b1Encoding key is not recognized by the electronics
d7Defective gas valve
02

What Fails Most Often on Bosch Junkers

Grouped from the official meaning of each of the 66 codes above — not from opinion. The number is how many different fault codes point at that component.

ComponentCodesExamples
Ignition16202, 2052, 227, 228
Temperature Sensor111022, 1065, 1075, 212
Flow Sensor91073, 1074, 2963, 2966
Fan8214, 215, 2942, 2961
Flue3208, A3, E9
Gas Valve3234, F0, d7
Pump3281, 2947, A1
Mains Voltage32943, 2972, 356
03

Parts & Prices

The parts most often involved in the Bosch Junkers faults listed above.

Ignition / spark electrode
OEM Part · Bosch Junkers
Check price View price
Temperature sensor (NTC)
OEM Part · Bosch Junkers
Check price View price
Flow temperature sensor
OEM Part · Bosch Junkers
Check price View price
Fan / blower assembly
OEM Part · Bosch Junkers
Check price View price
Compatible Ignition / spark electrode
Compatible · Generic
Check price View price
Compatible Temperature sensor (NTC)
Compatible · Generic
Check price View price
Compatible Flow temperature sensor
Compatible · Generic
Check price View price
Compatible Fan / blower assembly
Compatible · Generic
Check price View price
Reconditioned Ignition / spark electrode
Used / Tested · Bosch Junkers
Check price View price
Reconditioned Temperature sensor (NTC)
Used / Tested · Bosch Junkers
Check price View price
Reconditioned Flow temperature sensor
Used / Tested · Bosch Junkers
Check price View price
Reconditioned Fan / blower assembly
Used / Tested · Bosch Junkers
Check price View price

Prices and availability vary by region and are shown by the retailer, not by TroubleAtlas.

04

Diagnostic Tools

What an engineer uses to work through the codes on this page.

Digital Multimeter (TRUE RMS)

For testing electrode resistance and PCB voltages

$35–$80 View price

Gas Leak Detector

Essential for checking connections after any gas valve work

$25–$45 View price

Manometer / Pressure Gauge

To measure gas inlet and burner pressure

$40–$90 View price

Combustion Analyzer

For verifying flue gas readings after repair

$180–$350 View price
Full HVAC diagnostic toolkit
05

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Considering a New Heating System

Considering a New Heating System?

If your Bosch Junkers appliance is over 10 years old, replacing it with a modern condensing boiler or air-source heat pump could cut energy bills and remove the recurring faults listed on this page.

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Written by TroubleAtlas Technical Team · Last updated: 2026-08-02 · Sources: manufacturer service documentation · How we verify
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