Heat pump system

A heat pump system comprising:

• a compressor configured to compress refrigerant;
• a first heat exchanger configured to exchange heat between the refrigerant compressed by the compressor and a heating medium;
• a second heat exchanger configured to exchange heat between the refrigerant compressed by the compressor and the heating medium;
• a first pipe through which the refrigerant is fed from the compressor to the first heat exchanger;
• a second pipe through hick the refrigerant returns from the first heat exchanger to the the compressor;
• a third pipe through which the refrigerant is fed from the compressor to the second heat exchanger after returning from the first heat exchanger;
• and
• a switching apparatus configured to switch a flow of the heating medium between a first mode and a second mode, the heating medium flowing through the first heat exchanger and the second heat exchanger in series in the first mode, the heating medium flowing through the first heat exchanger and the second heat exchanger in parallel in the second mode,
• wherein the switching apparatus includes a four-way valve having a first port, a second port, a third port, and a fourth port and a check valve configured to prevent a backflow, and
• the four-way valve is configured to switch between a first state in which the first port and the second port are communicated with each other and the third port and the fourth port are communicated with each other and a second state in which the first port and the fourth port are communicated with each other and the second port and the third port are communicated with each other.