Furnace stopped working. thermostat shows system is on, but it isnt. Gave a kick;worked. tech says b

the thermostat is programmed. When I came home, heat was not running. Checked the thermostat and it shows system is on. Checked all switches everything was on. Went to furnace and opened the doors etc... nothing.. put the doors back and gave it a kick and it worked. Called tech, he says faulty switch and it will die on me again. He says part is free but $100 to install.

The unit is 3 years old. 02/2004.

Furnace stopped working. thermostat shows system is on, but it isnt. Gave a kick;worked. tech says bad switchmusicals

Hate to break it to you, but by reading what you did I had to laugh. Not at you but at the circumstances you described. The kick didn't fix it, taking the door off and putting it back on did. What you did is reset the control board by cutting the power to it. What is really happening is very normal. Im guessing at this one, but because you have a newer furnace, they all come with a flame rod sensor. Every time a furnace calls for heat there are a few things that happen in a specific order for the furnace to run.

1. Inducer motor will start up. (little fan near top of furnace)

2. This fan running will create preasure in the vent that is tied to a pressure switch.

3. This pressure switch will close which will in turn start the hot surface ignitor.

4. The hot surface ignitor will start to glow, some within 2-3 seconds and some almost 30 seconds. This is to ignite the gas.

5. At a specified number of seconds the gas valve will click and open.

6. Flame rod sensor has about 2 seconds to verify flame through a very small Millivolt current generated by the flame itself.

7. If flame rod sensor does not detect flame (could be dirty) the control board shuts off gas valve.

8. At this point the fan will be turned on and blow cold air.

9. If this condition happens 3 times, the furnace will lock itself out and not work.

10. You reset power and computer is rebooted and starts whole sequence over again.

In other words watch what the furnace does, if any of these symptoms happens according to the sequence of operations then you will know what is happening. I'll bet dollars to donuts all you need to do is clean the flame rod sensor with a bit of sandpaper. :P

Furnace stopped working. thermostat shows system is on, but it isnt. Gave a kick;worked. tech says bad switchopera songs opera theater

Could possibly be the door switch, as the tech said. that is a lot of money to install a door switch, I would tell him to get the switch which he is getting under the five years parts warranty, and install it yourself. It consists of two wires and when you unplug the unit, you will not have to worry about the power.
The switch could be fine, could just be that the bottom door was not on right or all the way. I would wait until it happens again before spending any money. Not too comon for a door switch to go out.