The invention relates to an anti-freezing control method and
system for failure of a four-way valve of a
heat pump water heater. The method includes the following steps that firstly, whether the current
water temperature T of the lower middle portion of a water tank is lower than the minimum temperature Tmin of the water tank in use or not is judged, if yes, the second step is executed; and if not, the first step is executed in a cycle manner; secondly, whether the descent speed Td of the current
water temperature T is larger than or equal to the preset speed
delta T or not is judged; or whether the current
water temperature T satisfies the
inequation of T<Tmin-a and is kept for the first time t1 or not is judged, wherein the a is the
temperature difference limit value; if any judgment result is yes, the third step is executed, and if not, the first step is executed; and thirdly, a
heat pump system is stopped and an
electricity auxiliary heating system is started. By judging whether the descent speed Td of the current water temperature T is larger than or equal to the preset speed
delta T or judging whether the current water temperature T satisfies the
inequation of T<Tmin=a and is kept for the first time t1 or not, whether the four-way valve of the
heat pump water heater fails or not can be judged precisely, and the error judgment situation is avoided.