My wife and I bought a rather old house this summer and discovered this winter that the furnace doesn't really work all that well. I have looked at it as much as my extremely limited knowledge has let me, so figured I'd ask here. We noticed that it was getting worse and worse as winter went on, with the weather warming up not really helping matters. I finally checked the filter and found it to be horribly dirty, so I replaced that immediately, without much help. The furnace runs. I have confirmed that it lights and burns, and the blower blows. I can see and hear all that. However, the vents on the first floor of the house blow barely warm air and hardly any amount of air. The vents on the second floor actually seem to blow slightly stronger, but blow cool-to-cold air. The furnace also seems to only run for 4 minutes(almost exactly) at a time before shutting off. It seems like something serious is wrong, and it is probably at the end of it's life, but I wanted to get see if there was anything else I could check before having a furnace repair person out to look at it.

OK I am not sure what to check as I replaced the igniter How can I tell if it is the igniter? Can I check to see if it is getting the voltage needed or is there another way? I did replace it a couple of years ago with a thicker unit? The fan continues to run and also I did not see any blinking red light.