The furnace doesn't heat anymore. It happened after a long (about 5 hours!) lack of power in the whole neighborhood. the unit is starting the little fan AND the heat blower in the same time but will not ignite the gas. The error code is 4 and according to the label on the control unit it says "OPEN HIGH LIMIT SWITCH" i CECKED OUT ALL THE SENSORS, AND SWITCHES AND FINALLY, i FOUND ONE, LOCATED SOMEHOW INSIDE THE HEAT BLOWER. i BYPASSED AND VOILA, MY FURNACE IS WORKING AGAIN. NOW, i KNOW THAT IT WILL TAKE SOME TIME UNTIL i WILL BE ABLE TO FIND THAT SENSOR BUT MY CONCERN IS ABOUT IF MY BYPASS WILL POSE A SAFETY ISSUE ON MY FURNACE