I need to know how to fix furnace no heatproblems. Everyone is giving me a literal cold shouldernow. Make sure the thermostat is set for hotterthan it is right now. Of course it is. If the thermostat is out of calibration orthe metal strip in it is bent so far it has to bend farther to reach the on switch forthe furnace, it thinks right now youre warm enough and wont turn on until it thinksit is ten degrees too cold. You want me to set it to 80 so it heats thehouse to 70. Just rule out that it is or isnt the thermostatbefore you start calling in expensive HVAC repair people. I might as well turn it off and back on totry to fix it. You can do the same thing too, if the furnaceis erroring out and thats why it wont run. I didnt think to see if the control boardhas any error messages.If it gives you any error messages like heyI dont have enough air intake, sensors say I shouldnt be running or electricalshorts, you will then know why it isnt running. What do I do if there isnt an obvious errormessage? If there is a wiring short or detached wiringfrom the control board to the ignition, it wont be able to ignite. If I have a wiring short, it could short outand burn up. If it has a loose connection or broken connectionto sensors, it thinks it shouldnt ignite or turn off.Thats almost what I want to have it be,because it is easy to fix. Then theres the possibility it is tryingto run but cant stay running because there is a problem. Like what kind of problem? It is overheating because it gets too muchair or has too much gas coming in, so it turns on, overheats and turns off. Thats like a flame sensor that is defectiveor dirty, so the furnace turns on and almost as quickly turns off. You can clean the flame sensor gently witha metal scrub pad. It is hard to imagine scrubbing it gently. If you break it, youll need to replaceit. Or I can replace it now. That is necessary if it has cracked or otherwisebroken. I cant imagine how it got broken. The last time someone replaced it, they brokeit against some metal piece in there. Or the last time they moved it closer to theflame to make sure the furnace recognized the flame was on they broke it.The flame sensor thus could be why the furnacewont run long, because it thinks the flame isnt running. Then there is the possibility it is runningbut not very well. I cant imagine how. If there are leaks in the air distributionsystem, that could cause it. So could blowers not working to distributeheat through the system. I’d notice that from the silence. So the issue is down to problems with thegas supply or valve to control it or sensors controlling the system. All of which I want a professional to lookat..