Ive got a 250gal lp fuel tank. My central unit is giving some major problems after a lighting storm came through. The tech. came out and replaced a defective motor on the unit but is still having problems with the heater staying lit. My tank is at 20%. The tech. is now saying that it is the fuel tank level. He's saying it doesn't have enough pressure at 20% to run correctly. Is this right?

As long as there is one drop of liquid, the system will be at the vapor pressure of the liquid up to any regulator of orifice. I guess when the tank is low, it might not absorb heat fast enough to keep the liquid from being cooled as it evaporates. Cleaning the bottom of the tank and assuring air flow should take care of that.

Once all the liquid is gone, the pressure will drop like a rock.

I think the tech's plan is to delay until the tank is refilled, and hope somebody else is sent out. At least he will buy himself more time to think about it.