Possible reason:
1. The tank is empty
2. The pipeline or the connector falls off or is blocked
3. In the winter , water in the feeding/outgoing pipe may become frozen
4. The vacuum tube is damaged
5. Tap water supply stopped or low water pressure
Solutions:
1. Add water according to the tank
2. Maintain the pipeline or remove the blockage
3. Start the accompanying heating strap or wait for natural ice-out
4. Replace the tube
5. wait for normal water supply