Hello everyone, first use of the forums, unfortunately.
So the problem is that I have a Lennox Pulse21 of unknown age in my home I purchased several years ago and never had any trouble with it until this current winter about a month ago. I installed a newer thermostat on it for some features, but it was before last winter and has had no problems there as far as I know.
The furnace has been doing a wierd series of problems where it will not kick on unless our thermostat is set for a much higher temperature than it normally would * to something like 3-5 degrees higher than the room temperature it * and in addition to this it often shuts off soon after coming on. Sometimes I hear it click, run for a bit then shut off before it heats any. The fan will kick on a lot and if any heat fires up it's for a very short time. I can sometimes trick it into coming on by shutting the thermostat to off, flipping the pilot to off then back to on soon after * PILOT option, it's just on or *, but these methods don't always work, or it waits 10-15 minutes before it fires up. I found a new trick that I can drop the temperature below the listed room temp, then increase it and it sometimes will work.
From what I understand this unit does not have a thermocouple? I read about a flame sensor, which I assume does nearly the same thing just by a different method. I know where the spark plugs are located but haven't checked them, and the condensate line seems to work properly, but can be rechecked if that's a strong suggestion given.
Anything to try is better than nothing, and the tricks seem to be working less and not as quickly every time. I'm not familiar with furnaces so if you can explain in details that would be much appreciated.