Make sure main boiler fuses are correct and if they are automatic, ensure they are furnished to the ON position. If fuses are correct, check the fuse on the boiler controls.
Check if safety thermostat is out for some reason, and if so, reset it. Other reason could be that your room thermostat is set to some temperature and if room temperature reached temperature set on room thermostat, then room thermostat switched off heaters.
Check if all heaters are turned on and if thermostat on boiler is set up to desired temperature. Call a qualified person to check whether the boiler has three phases. Make sure the heating system have excess air and, if necessary bleed the entire system. Call a qualified technician to determine whether all heaters correct.