The furnace in my house is having a problem. The furnace overall works well and heats the house fine. The problem is that it cannot turn itself on. There is a Nordyne vacuum switch on it that is supposed to test whether or not it is being ventilated properly. It works by itself about half the time, but other times I need to go down and connect the two wires that come out of the vacuum switch with a jumper wire. Then it makes the furnace think that it has the necessary vacuum power and starts up. However, when it is bypassed, after it reaches the desired heat on the thermostat it goes off but will not turn back on until I unhook the bypass wire. This makes sense and is not really what I am asking about, it is just what I do. I have gone through three vacuum switches of the same model and they all have the same problem. Here is a basic routine of what happens every time:

• The temperature in the house goes below 67 degrees, and the thermostat tells the furnace to turn on.
• The exhaust fan on the furnace turns on, along with the red LED on the main board.
• It runs for about 10 seconds.

This is where a few different things happen. If the switch wants to work, then this happens:

• The furnace makes a click, and then the glow plug starts up.
• The glow plug heats up.
• The furnace clicks again, and the gas kicks on. A yellow LED on the board turns on as well.
• A few seconds later, the blower turns on and starts to heat the house.

However, if it is completely not working, then this happens:

• The red LED on the main board of the furnace starts flashing a pattern like this: On, Off, On, Off, On, Off, On, Off, and then stays off for a few seconds and then repeats. Here is the pattern visually with 0 being off and 1 being on: 1 0 1 0 1 0 1 0. This loops forever until I turn off the furnace either with the main power switch on the back or by telling the thermostat that I do not want to heat the house anymore.

Another thing that happens sometimes is the switch kind of works and kind of doesn't:

• The furnace waits more than 10 seconds, usually around 20 or 30, and then starts the glow plug.
• The glow plug heats up to maximum power.
• The furnace clicks twice like it is trying to turn on the gas, the glow plug goes out, and the burners do not turn on.
• This sequence repeats without getting anywhere.

As I said, I have tried 3 vacuum switches, and the same thing happens with all of them. The furnace was put in when the house was built, so about 13 or 14 years ago. I have tried a lot of different things and some researching, and I could not come up with anything. I don't know if it is the vacuum switch that is giving me the problem, or maybe the circuit board or one of its relays, or maybe the ventilation pump. I am really hoping to be able to fix it without needing to replace the whole thing. My question is if it seems like I have defective vacuum switches, if the board is bad, or if there is something else I need to check on.

(Note, I will try to get some information about voltages and things when I get a chance, and maybe a picture of the inside of the furnace.)

Edit 1: The label inside the furnace says the model is a "Nordyne FG6RC 080C – 168"

Edit 2: The problems have been happening for about 5 years. Last year the two inch pipe for air input was replaced with a three inch pipe.