Why Won't My Heat Turn Off?
An AK employee asks: My thermostat (like the one seen here) has been set to a constant 68 degrees. Today, for some reason, the heat just keeps running and the temp keeps going up and up and up. The batteries are new and I've tried tapping it ;)
The heat will go off when I turn it to off. But no matter what temp it's set on, when you turn it on the heat will just run and run. Anyone had this problem? HVAC experts?
If this happened right after the batteries were replaced, remove the cover and check the base plate for crossed white and red wire. They may have been bumped together when the cover was replaced. If that is not the issue, while the thermostat is off of the wall, leaving the base plate and wires intact and the furnace stops, then it is the thermostat and it needs to be replaced. If the heating system continues to operate, then the issue is at the furnace. Not knowing your heating system I would assume it is fairly new? Perhaps under 20 years? If so, you may have a printed circuit board that is faulty. Many of these boards have a light, red/green that blink on and off in patterns. This blinking pattern will tell you if something is wrong or not with the system. Some furnaces have observation holes in the blower door panel that you can look into in order to see the light. Others require you to remove the blower door panel to access this board and light. If the latter is your system, remove the door, then hold the door switch in that will keep the system running and watch for the blinking pattern that is showing up. On the inside of that blower door in most cases you will find the directory of the blinking patterns telling you what if anything is wrong. If that checks out OK, then the issue is with the thermostat wires being crossed somewhere. Each wire has a function. Red wire (R) is the low voltage feed from the transformer. White wire (W) is the feed from the thermostat to the gas valve. When the red and white wire is connected together it turns on the gas valve and calls for heat. If your really brave, look for those wire connections on the furnace. You will see (R) (W) (G) (Y) and a few more possibly depending upon your unit. But if you take off just the white wire from under the screw and the furnace keeps running, It is for sure either the control board or the gas valve becoming stuck on. Just be sure to turn off the power of the furnace when removing wires. Although only 12 volts, if you accidentally short them it will burn out the transformer in a flash.
If your heat won't turn off and your thermostat is operating properly (quick check, disconnect it from the wall or take the batteries out) then most likely your valve(s) is/are stuck on. There is a manually lever that you can use to manually open or close the valve. To note, this can go both ways too. If your heat is not coming on when your thermostat sends the command, then it is most likely a stuck valve. Look up "heat valves" or anything along that line and you will get some good literature regarding the most likely cause of the problem. ALWAYS PROCEED WITH CAUTION IF YOU ARE NOT COMPETENT OR CERTIFIED TO PERFORM DANGEROUS REPAIRS OR MAINTENANCE. REPAIRING A HEATING SYSTEM IS DANGEROUS AND SHOULD BE REPAIRED BY A PROFESSIONAL
I think there is some problem with the sensors. I don't think you will be able to handle the task all by yourself if you don't have any prior experience. I would recommend calling an expert AC service professional. Hope it helps.