Old Bard not getting hot

[richb]

I'm having a problem with an older Bard furnace. Yesterday the pilot wouldn't stay lit, so I replaced the thermocouple. Still wouldn't stay lit. So I started playing with the controls on the main gas valve to see if that would work. Eventually, after cleaning the copper part that shoots the pilot onto the thermocouple, the pilot stayed on. Unfortunately, now the blower short cycles. The furnace is on all the time, but the blower kicks on and off. It seems that it's just not getting hot enough. If I manually set the blower to "on", after about 30 seconds I get mildly warm air blowing through the ducts. If I set the blower to "auto", it will run hot for 30 seconds and kick off. I have spent the better part of a day and a half adjusting the pressure regulator on the main valve, but I just can't get it hot enough. I called out a hvac technician, who recommended I replace the furnace. It's old. He doesn't work on these things. Which I understand, but I have a feeling this is something minor. Any ideas?

[richb]

I called another technician out expecting to hear the furnace needed to be replaced, but this gentleman noticed right away that I hadn't replaced my filter after I cleaned it. Put that back in, and voila! The air was moving through too quickly without it, knocking the temp down too fast, which made the limit switch cut the blower off. I felt a little silly, but knowing there are honest people in the world makes it all worthwhile.