[rnln]

update....
I just went down to look at it, and plugged it back in (it's unplugged). Soon I plugged it in, everything back to normal, both power and output lights are on). Pump is running. So it fixed itself after a a day unplugged?

I feel like the solar tank is getting cold water from source by pressure as any normal devices. The pump function is to pump water up to the solar panel (on the roof).

How water get from solar tank to gas tank? My pressure in the solar tank? Meaning if the pump is turned off, no water get to the roof, then no water get down from the roof to the solar tank, meaning no water is going to the gas tank? And if I keep using hot water (without the pump running), I will dry burn the gas tank? Am I correct? or the solar system has a way to supply water to the gas tank without going through the pump? Then there must a valve somewhere to detect if the pump is working properly or not?