I have an armstrong ultra sx-80 gas furnace my problem is when I turn the unit on it will start up fine when I set it to heat, run for a few minutes then the flame dies. The blower stay on and will not shut off until I unplug the unit. The heat never reaches it's set point. If I wait for about 30 minutes plug the unit back in the furnace will fire up just fine and then shut off after a few minutes keeping the blower on until I unpulg the unit. I know the blower stays on to cool every thing down after it reaches it's set point but that's not the case cause it never reaches that point. Any help would be great. Thanks.

If the flame ignites and then drops out I would look at the flame sensor. Take it out and clean it. As far as the fan running, modern furnace blowers are not actuated on time and not temperature. On a call for heat there is a time delayed relay that will turn the blower on.

I am having this same problem, I am 100 percent stupid to heating systems and don't know were the manual is (I'm in this new town home) is there any resources that I can find?

I have an amrstrong ultra sx 80 propane furnace, my question is, is there a way or insert to make this an electric heater?

http://www.selfhelpforums.com/showthread.php?t=715

A friend of mine just spent $100 having her Armstrong Ultra SX-80 furnace fixed. According to the repairman, this is a common problem with this model and is easily fixed by the homeowner -- so I thought I'd post the fix here and, hopefully, save some future reader a few bucks.

Her problem was that the furnace would not light. This unit has an electronic ignition that will not function unless conditions are OK in the combustion area. When the thermostat calls for heat, the combustion fan motor turns on, drawing in fresh outside air. The pressure caused by the fan is detected by a separately mounted pressure switch. If the switch is not activated, no ignition.

The pressure switch is connected to the combustion area by an 18 inch length of 1/4 inch rubber hose. It turns out that there is a lot of condensation in the combustion chamber in the area of the hose fitting and particles of rust can clog that fitting. Once the serviceman realized the pressure switch wasn't activating, the first thing he did was pull the hose off the fitting near the fan and ran a wire down the fitting bore to clean it. He reattached the hose, hit the power switch and the furnace fired right up. Total time: 10 minutes, tops.