Another issue concerning ecology of the small-scale boiler operation is validity of signals provided by the key sensors that are used for control of the boiler. There are two of them that are of the main interest – the temperature sensor and oxygen sensor. For the case of the experimental boiler, there have been used for newly designed continuous control the temperature after first convective section of the boiler (marked as T2 on Fig. 3) and oxygen concentration, measured by a lambda-probe (marked as CO2 on Fig. 3)