Service recall: maintenance performed less than 30 days ago Found no 120V power coming into the furnace Disconnect switch failed from having the wires stabbed in rather than wrapped around the screws Bypassed failed switch Furnace would still not power up despite having 120V to it now Verified 24V at transformer secondary Pulled 3A fuse from the control board, it was blown Checked for short circuits with Ohm meter, nothing found Replaced fuse and powered on furnace It went through its startup routine and when it energized the gas valve, the fuse blew again Replaced gas valve and fuse Set gas pressure to 3.5"wc Furnace operating normally at this time