Hi, do you have the calefont, is it new or is it used? I think it is used, the fault is due to the flame sensor that is sulfated. in that case what I recommend is to do a preventive maintenance to leave the whole system ready. If the heater is new it is likely that the gas pressure is low and the flame sensor has been sulphated by poor combustion. the sensor should be changed at the same time as increasing the gas pressure to the rule, more or less must be between 18 to 25 mbar. stay tuned!