New Weil McLain eco tech 110 install

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I am replacing, believe it or not, an outside pool heater with a new Weil McLain Eco Tech 110 boiler to provide hot water to two heater cores in two different air handlers (two different zones). Some back story I am not a HVAC technician but I am an automtive and diesel technician that is trying to replace a failing pool heater. I've got the Weil McLain Eco Tech 110 installed, when commanding heat from the no. 1 zone thermostat (I do not have the 2nd zone thermostat wired in yet) it burns the 3 amp fuse on the circuit board after a few seconds. I have the "R" and "W" wires run from the air handler to the boiler and have tested at the air handler, when heat is commanded both wires show 24V. I am hoping someone can lend any ideas why it may be doing that. I do notice on the instructions the input mentions "External 0-10VDC. I may be missing something but the thermostat is clearly putting out 24VAC.