On the first cold day after his visit (four days after the service visit), the furnace started acting up. This is what happens:
1. There is a click in the gas control unit 2. The flame starts, and it looks clean (ie blue with very little yellow), at least from what I can see through the inspection hole. 3. A few seconds later the fan starts 4. A couple of seconds after the fan start, I hear another click, and the flame goes out. 5. The fan stops after about one minute. 6. After about two or three minutes, the cycle starts all over again.
As a result, there is hardly any heat. I figured that this frequent on-off cycle every 3 minutes is not good for the unit, so I turned the whole thing off. It has been very cold, so this problem needs to be fixed soon.
I find it very strange that the problem started on the first cold day after the service visit. I called the company that serviced it, but he said there will be a service charge for him to look at it again unless the problem can be traced to his work. Of course, since I don't know much about furnaces, I can't prove that it was his fault.
From the little I know, this sounds like a problem with the flame sensor. If it is indeed the flame sensor, can I reasonably expect that he should have inspected that during the service? I am inclined to think that the furnace would be working fine today if I had not had it serviced.
Any advice on how I should proceed?