Our furnace started blowing out only cold air and the fan seems to run even if the thermostat is off, we tried replacing the thermostat and that was not the problem. It is a tech-4 gas furnace True blue 90. We were told it was the ignitor and that our model would also need to have an additional valve replaced. Do you have any knowledge if this could be replaced without a service technician as this would be the cheaper way to go I am sure. Any help is appreciated Thanks.

Call a qualified service person to effect the repairs.