We have an intertherm furnace. The led light is blinking twice meaning that the pressure switch is open. We have replaced the pressure switch and are able to blow air through the attached tubes. They seem clear. The light continues to keep blinking.

Are all vents,supply and return open and clear? Is filter clean? Is it possible anything could be clogging the exhast vent? Does it have a clean a-coil?, this will keep you buisy for a while, get back to us