I have a Lennox G16 series electronic ignition heater circa 1987. The full model number is G1603x-50-5. The problem I am having is that the heater turns on, the furnace is lit, and then a short time later the flame goes out and it restarts the process. This continues on with the same cycle. When I first turn it on the heater will go on and stay on for several minutes. However, after awhile the cycles start occuring one after another. Unfortunately, I don't have a manual. Any thoughts?

Hi, I have a Lennox OHR-2303/4-105/120-4c furnace - only a couple of years old. There _are_ issues with the ductwork, which I am trying to address (under a crawl space, critters got into the ducts and I'm having to patch things up). BUT, this is not my main problem right now!!! The furnace will kick on, followed by the blower in approx 2 minutes, but the supply air coming out at the furnace itself is not getting much above the mid-80s. There is a nice blue flame produced. Any suggestions? There may be a lot of insulation and other garbage inside the return lines, but that doesn't seem like it would keep the air that is getting through the furnace from heating up. I am expecting supply temps of over 100F at least - is this a wrong expectation? Thanks! Scott