Your boiler is recalibrating how it mixes gas and air for burning, which sometimes needs a reset, but if it keeps showing this code, a qualified engineer should check it.

Fault Eb. Automatic calibration of the combustion controller. Measure: Check gap between ionisation electrode and burner gauze assembly. Check allocation of gas type (coding address 82, gas train setting). Check flue system; remedy flue gas recirculation if required. Press reset button R.