Sump pump battery failed and exploded setting off CO detector due to chemicals in the air. Gas company was unsure of original source and wanted furnace inspected, but upon second inspection due to alarm sounding with the furnace off they discovered the sump pump battery. Gas heating preventative maintenance performed Check filter - 20x25x1 9/8/25 Clean flame sensor Ohm test igniter: 56.8 Inspect wiring for loose connections and/or hot spots - none found Check humidifier pad: N/A Inspect exhaust flu - no concerns - burn marks from torches on install removed. Set thermostat for heat Check amp draw on blower motor: 4.68 Check amp draw on inducer motor:0.96 Check delta T - 53° Furnace is in optimal running conditions