Water flow detection method, device and system for hot water machine unit

The invention discloses a water flow detection method, device and system for a hot water machine unit. The water flow detection method comprises the following steps: an inlet water and outlet water temperature difference of the hot water machine unit at a first environmental temperature is acquired, wherein the inlet water and outlet water temperature difference is the difference of an inlet water temperature and an outlet water temperature of the hot water machine unit at the first environmental temperature; whether the inlet water and outlet water temperature difference is larger than a reference inlet water and outlet water temperature difference, the reference inlet water and outlet water temperature difference is the difference of the inlet water temperature and the outlet water temperature of the hot water machine unit at the first environmental temperature and under the condition of standard water flow; the water flow of the hot water machine unit is determined to be smaller when the inlet water and outlet water temperature difference is detected to be larger than a reference inlet water and outlet water temperature difference. The water flow detection method solves the technical problem that the service life of the hot water machine unit is shortened due to the fact that smaller water flow of the unit can be detected only when the hot water machine unit reports a high-voltage fault in a correlation technique.