1. Close both valves.
2. Open the faucet which can put hot water on the hot water side.
3. Open the two water valves respectively. Water should flow from the faucet which releases hot water.
4. Try turning off a water valve. If no water is flowing from the faucet that releases hot water, that water valve is responsible for the hot water. The other takes care of the cold water.
Let's first see how the solar water heater pipes are connected. 1. The water addition valve and the heat valve are two independent valves, but they are one pipe (at the bottom of the water heater) leading to the solar water heater. So, after filling the water, you need to close the water fill valve. 2. Generally, the pipe that overflows when water is full is at the top of the water heater, and water will flow out when it is full. It looks like your valve is probably the main valve connected in series in front of the valvewater supply. You should know its uses without reading the previous description.