Lao Guo good man!. I repaired one similar unit, changed whole heat element and conttrol. The parts 2x4000kw was about 30 some dollars. You need electric meter, and one (special) wrench. If some one is interested in doing by yourself, put discussion here in 168. I am repairing my upstair furnace unit now. If successful, I will let u know. The electric igniter does not work.