My brewery has a 10 gallon capacity so my kettles are 15 gallons. My problem is adequately managing mash temperature. Direct heat doesn't work because the false bottom can act as a barrier to heat flow, I don't like recirculating the wort, and I have tried a heat exchanger (copper line) in mash tun but the pump works well at lower temperatures but when I raise the temp in the hot liquor tank the pump seems starved and nothing flows. I have increased the size of the line feeding the pump and the pump is below the hot liquor tank. So what's going on?