I have been having a problem with my Lennox furnace. For the past week or so it would go into watchguard mode and I would fiddle with the thermostat to get it to turn back on. It would turn on and heat, but then after a couple of cycles it wouldn't come back on. Now it isn't turning on at all. I checked to blinking light code and got Watchguard mode - burners failed to ignite. When I try to restart it the starter glows red, then the burners ignite for about 3/4 of a second and go out, this repeats about 4-5 times and then it goes back into watchguard. I tried cleaning the flame sensor, but that didn't fix it. Anybody have any idea what might be wrong?

[FONT=arial]A little over a week ago I had to have a new Draft Inducer installed on my Tempstar furnace. Since then it will work from a few hours to about a day. And throws an error code about [/FONT][FONT=arial]pressure switch stuck open when should be closed[/FONT][FONT=arial] . When the repair man installed the Inducer he did not install the new seal that comes with it. I know this because he left the bag of spare parts laying on a counter by the furnace. Could him not replacing this seal be causing the error code? [/FONT][FONT=arial] This evening I took the inducer out and replaced the seal the other one looked rather used. So I am waiting to see if this fixes the error. I have done every thing that is mentioned on line about cleaning tubes and hoses, cleaning intake/exhaust pipes, drain trap, condensation pump and even replaced pressure switch. Still furnace would run for a day and throw the error code. Any thought or suggestions would be greatly appreciated.[/FONT]