My central heating unit at my house blows cold air when I switch to heat. Unfortunately, it worked fine when the serviceman came out to inspect it two days ago. Three weeks earlier, the same guy went up in the attic and lit the pilot that we turn off during the summer months. When he did that everything worked fine for about three or four days only. When he returned a few days ago he checked the same pilot light to see if it had blown out but it remained on from the first time he lit it. Then the heat worked fine for the next hour. One day after he left it started blowing cold air again. Things don't work when the serviceman is away. As soon as he comes the problems go away. What could be going wrong with my central air/heating unit?

Please contact me at [email protected]

Thanks,

Tom

Check the sensors

If it is a old style thermocouple system then the thermocouple could be bad or the pilot lite orifice needs to be cleaned.