... design 2.SD series: Anti-dirty monothemic heat exchanger, LED display temperature and combustion power, Timely error diagnoses, buzzer alarm, ... Microcomputer digital control 3.SP series: Bithermal heat exchanger, LED display temperature and combustion power, Timely error diagnoses, buzzer alarm, Microcomputer ... devices ensure normal operation in bad quality area Gas Wall Hung Combination Boilers