gas furnace shuts off too soon

______________________________________________________________________ While on a service call I experienced that the furnace turns on but shuts off before the home gets warm. It lites up correctly with blue flame. It shuts off and the blower blows for about 2 minutes and then shuts off. This is good so far. T-stat is new and works properly. Wires on the control board are all connected correctly, and the limit switch breaks the circuit when it gets too hot in the unit. Filters are clean. But the furnace shuts off before it heats the house. What can be wrong? What do you think? Replies: toleary “Re(1):gas furnace shuts off too soon” , posted Fri 4 Feb 10:45: ______________________________________________________________________ Is the stat level? If it is standard mercury bulb this would cause problem. Is the anticipator set correctly? Set to furnace current draw. Trainer [this message was edited by toleary on Fri 4 Feb 10:46] Freon “Re(1):gas furnace shuts off too soon” , posted Thu 3 Feb 16:20 ______________________________________________________________________ Under normal operating conditions, how close is the indicated room temp to the set temp when the burners go off? Assuming you get within 2 degrees of the set temp (ie the set temp is 70 and the burner goes off at 68), try changing the set temp to 80 degrees. Will the flame go out at 78? If so, I’d suspect the thermostat calibration. If the flame goes out at a lower temp like 74, then I’d suspect a faulty limit switch. tinner73 “Re(2):gas furnace shuts off too soon” , posted Thu 3 Feb 19:44 ______________________________________________________________________ what does the evap. look like? is it clean or clogged? if it’s cutting out on high limit there’s probably an airflow issue.