Weil-McLain, of Michigan City, Ind. voluntarily recalled about 1,800 Williamson-Thermoflo GWS and GWI Gas Boilers. If there is a leak in the vent piping, the recalled boilers can leak carbon monoxide (CO) into the buildings in which they are installed, posing a risk of CO poisoning. The recall involved certain cast iron, gas-fired boilers used for space heating. These products wer e sold by plumbing and heating wholesale distributors to plumbers and contractors nationwide from October 2001 through December 2007 for between $1,500 and $2,700.