The circulating fan in my Miller furnace won't turn on when the burner has been lit for an extended amount of time.I checked all the fan control switches all seem to be operating properly.I have power from the transformer . The furnace has a manual switch which when used makes the fan turn on but not with the burner.
Any ideas
What might be the problem? Anyone have same issues? I need help getting cold.

Could be a defective fan control
Could be a defective fan relay if used.
Try turning the heat on and running the blower manually. That should work till you get it fixed.

If I read your post correctly, you already tried to use the fan on position, and it didn't work. Some furnaces are wired up that way. The fan on and A/C often use a different motor winding and relay for higher speed than heat.

If you have limit switches controlling the fan, likely you have a separate relay, or combined with a transformer in a fan control center. They are much easier to troubleshoot and repair than the new furnaces with a timer and relay on an expensive control board. Follow the motor leads back to the relay. There should be 2 of them, or 2 sections. You want the one connected to the limit switch, not the green wire from the thermostat. Once the limit switch closes, you should have 24 volts across the coil terminals. If you do, and the line has 120 volts, but not the load, the relay is bad. If the motor lead is hot and the fan doesn't run. Likely the heat winding is shot. Before buying a new motor, check all the connections.

To do simple checks like this you do need some tools. A test light, a meter, or a voltage detector might be the best place to start with. I came across the niftiest gadget for trouble shooting, a voltage detector. They work through the insulation of wires. There are several brands. I have a GB Instruments GVD-505A, less than $15 at Home Depot. Touch it to a hot wire, and the end glows red. Find the doodad that lights it on one side, and not the other, and you have the culprit. You do not have to open up housings and expose electrical contacts. You are looking at where your hand is, not where the meter is. Most people are capable of doing repairs and will get it going and not get hurt if they use a little sense. The voltage detector makes it even easier.

I found a spider had spun a web in the burner,blocking the full flow of gas.
The furnace never got hot enough to start the fan.
Alls working now.Thanks for any answers to my problem.