Furnace runs but blows cold

wa8yxm wrote:

enblethen wrote:
OPs furnace should have a flame sensor and ignitor, not a thermal couple.

Says you? The flame sensor as you call it IS a thermocouple.. I know. I tested mine. I am aware they are often called "Flame Sensors" but there are two or three types of flame sensors. ONE of them, the one Atwood and Suburan both use, as well as my water heater. Is a Thermocouple

Thermocouples use two dissimilar metals to generate a small voltage when heated that can be used to maintain the fuel supply for the flame. If it cools down, the fuel supply stops. Atwood and Suburban use thermocouples in their standing pilot water heaters, but not in their DSI water heaters, refrigerators, or furnaces.

Atwood and Suburban's DSI flame sensors work by sending a small current to the ignitor probes that is passed through the conductive flame to be sensed by the ignitor board where it's used to keep the fuel supply valve open. No flame, no current passes back to the board and the valve closes. A common flame sensor failure mode is that the burner lights and then quickly shuts off when the flame is not sensed due to misadjustment, dirt, corrosion, or board failure.