Water heater having secondary heat exchanger

A water heater, comprising:

• a combustion device where gas is burned to generate heat;
• a primary heat exchanger above the combustion device, and having a first case and a water pipe, wherein the first case has a first exit opening, and the water pipe is received in the first case;
• the water pipe has an inlet and an outlet;
• and a secondary heat exchanger above the primary heat exchanger, which is adapted for performing heat exchange between water and a high-temperature flue gas, and includes a second case having an enter opening, a second exit opening, and a bore, wherein the enter opening is communicated with the first exit opening of the primary heat exchanger;
• a heat tube set received in the case, and having an inlet and an outlet for water entering the heat tube set via the inlet and leaving via the outlet;
• a cover board detachably connected to the case to seal the bore;
• and a collecting member received in the case under the heat tube set;
• wherein the second case of the secondary heat exchanger has a plate at a top thereof and a board;
• the second exit opening is provided on the plate, and the bore is provided on the board;
• the cover board is detachably provided on the board to seal the bore;
• and the bore exposes the heat tube set wherein the collecting member has a top board and a low board;
• the top board is stacked on the low board, and a space is formed between the top board and the low board;
• wherein the water heater comprises a base and a main case, and the secondary heat exchanger is mounted on the base;
• the main case is detachably connected to the base;
• the cover board has an inner side;
• the collecting member has a front edge;
• such that a first distance is formed between the front edge of the collecting member and the board, and a second distance is formed between the front edge of the collecting member and the inner side of the cover board;
• and the second distance is longer than the first distance;
• wherein the cover board protrudes relative to an outer surface of the board of the second case, whereby to increase a space to be passed through by the high-temperature flue gas;
• the secondary heat exchanger further has a separating board connected to the inner side of the cover board, and an interval is formed between the separating board and the cover board, wherein the interval does not communicate with the space to be passed through by the high-temperature flue gas such that the high-temperature air does not enter the interval and can only be in contact with an inner surface of the separating board facing the collecting member;
• a third distance is formed between the front edge of the collecting member and the separating board, and the third distance is shorter than the second distance, but longer than the first distance to thereby guide the high-temperature flue gas flow generally upwardly through the space including the first distance and the third distance.