The water return pipe is blocked. Check the water return pipe. You can also extend the short pipe over the water return tee. If the water is full, you may not know it. First check if the watch is broken; if the watch is broken, replace it. If the meter is not broken, then the probe is broken. Simply replace the probe. My wife worked in solar energy. In most cases, the probe is broken.
Of course, this will affect the lifespan of solar energy. First of all, the return pipe has two functions. One is to work as a condenser pipe and the second is to work as a circulating water pipe. If the return pipe of the solar hot water pipe does not return water, it should be considered that the valve is closed, or the pipe is blocked by foreign objects, or the difference between the location of the water heater and the local atmospheric pressure when the energy installationsolar, that is, the pressure in the water pipe of the solar water heater is lower than the normal atmospheric pressure, may affect the operation of the return pipe.