We have an Armstrong Furnace Ultra SX 80. Model #GUJ100D12-3A, Serial #8499G36777, installed in the fall of 1999. We had some trouble last year and had a furnace tech out and he said we needed a bunch of parts. We have used the unit this year since the heating season began with no problem. We do not keep the furnace on all day. We heat it until it gets to 70 in the morning and then we turn it off at the thermostat. We may or may not heat it a few times during the day, or it stays in the off position until the next morning. We only use two fills of propane per year (500 gal. tank) due to the way that we use the furnace and the fact that we have the benefits of passive solar (lots of south facing windows) and excellent insulation
. We also have the good sense to put on a sweater if we're chilly! That propane is also used to heat water and cook.
Yesterday when I turned the furnace on in the morning, the exhaust fan started like it should, then the glow coil turned on, then heard the click of the gas valve, but the burners did not light. The glow coil turned off. Then the same process began all over again. I turned off the furnace at the thermostat. Then I unplugged the furnace from the wall (it's powered by a heavy duty three pronged plug and 12-2 w/ground house wire). When I did this, I heard a click (like the gas valve turning on) and then nothing. I plugged the unit back into the wall socket, turned the thermostat back on and voila! the furnace turned on like it should. We never let the furnace cycle for a second time, but today, we did, and the furnace turned on like it should.
My husband is a retired Columbia Gas Serviceman, and between us, we suspect either the control board (which I understand has had at least one revision) or the gas valve.
Can you tell with certainty which of these parts need to be replaced? If you need further diagnosis, I would be happy to correspond with readings from a volt/ohm meter if you will tell me the points to check between and what the reading should look like if it is healthy. We would love to have a furnace tech out again but we're afraid to get cheated by unscrupulous people, which we suspect these last guys of being.