The floor heating water inlet pipe is hot, but return pipe is cold. What happened?

The main reason is insufficient circulating flow. 1, check whether all valves are fully opened or the valve core cannot be opened. 2. Check whether the filter element is blocked and needs cleaning. 3. Is a heat exchanger installed at the floor heating water inlet, and is the heat exchanger blocked due to too long time? 4, heating pipe network system flow is not enough, you can ask neighbors, if neighbors have the same situation, indicating that there is a problem with system flow, you can find a heating company to solve it.