40 LED blinking: Overheating error. Check the water pressure in the system (should be 1.5 bar). If the problem persists, the heat exchanger, pump, or three-way valve may be faulty.
50 LED blinking: No flame detected. Check the gas valve and ensure gas is supplied to the boiler. If the issue continues, the ignition electrode or control board may be defective.
60 LED blinking: Flue prosestat error. There might be a problem with the fan, prosestat, or electronic board.
70 LED blinking: Prosestat or flue sensor error. The prosestat and flue system need to be checked.
40 and 50 LED blinking: Radiator NTC sensor fault. Check the sensor and connections.
50 and 60 LED blinking: DIP Switch settings are incorrect. Call technical support for adjustments.
60 and 70 LED blinking: Domestic hot water NTC sensor fault. The sensor and connections should be inspected.
40, 50, and 60 LED blinking: High-temperature increase in the heating circuit. The pump or bypass line may have issues.
40, 50, 60, and 70 LED blinking: Exhaust gas buildup in the combustion chamber. Inspect the heat exchanger and combustion chamber.
Bosch Classic Condense Boiler Error Codes
A7: Domestic hot water NTC sensor fault. Possible issues with the sensor or its connections.
A8: BUS communication interrupted. Check thermostat and connection cables.
B1: Code key not detected. Contact technical support for verification.
B2 / B3: Internal error. Expert assistance is required.
C6: Fan fault. Inspect and replace the fan or cables if necessary.
CC: External air sensor fault. Sensor or its connections need inspection.
D3: External temperature limiter active or connections are missing.
D5: External temperature sensor fault. Sensor and cables should be inspected.
E2: Flow temperature sensor fault. Inspect the sensor and cables.
E9: Safety thermostat or low-pressure switch active. Check water pressure and bleed the system.
EA: Flame not detected. Inspect gas supply and reset the boiler.
F0 / F1: Internal fault. Contact technical support immediately.
F7: Flame detected while the device is off. Inspect electrodes and exhaust gas path.
FA: Flame persists despite gas cut-off. Check ionization electrode and gas valve.
FD: Reset button pressed too long. Restart the device.
Bosch Classic Plus Boiler Error Codes
A7: Hot water temperature sensor fault or connection issues.
A8: BUS communication error. Check thermostat and connection cables.
B1: Code key not detected. Ensure proper placement or replace the code key.
B2 / B3: Internal error. Technical support is required.
C6: Fan fault. Inspect and replace the fan or cables if necessary.
CC: External air sensor fault. Check thermostat and connections.
