if the solarheater is in good coundition
There are system issues to consider also. For example, is this a closed glycol-system with a heat exchanger, or does it heat the water directly from the incoming supply? Glycol systems require a circulating pump and usually have a temp sensor on the collector to ensure that the water temp in the collector is going to contribute thermal energy to the heat exchanger. If there is sun and there is glycol in the system, check the circulating pump, controller and temp sensor. Also, if the system is not plumbed propoerly you can get air trapped which will prevent the circulation of the water. Pool heaters are similar but instead of glycol and a heat exchanger, there are valves that detect when the solar heater will add to the temp of the pool or spa, and the valves will open to circulate pool water through the collector. If the valves aren't working properly of the controller is malfunctioning, or there is air trapped in the system, it won't work. Also, the pump has to generate sufficient head (pressure) to raise the water up through the collector. If the pump is inadequate or there is a plumbing issue, the pump will run, but the water won't circulate. If the system uses supply source it relies on adequate sun exposure to heat the water in the collector resevoir before the water is delivered to the storage tank, usually a hot water heater. If the plumbing is done correctly and there is sun and time to heta the water, the resevoir temp will reach temps of over 120 degrees F. If not plumbed properly there can be other issues like described above. j
