hydro flame furnace 79/80 series

[87_Alpenlite]

Sorry for the long winded post but I felt it necessary.
I have a Hydro Flame Corp Everest Star 79/80 Series Furnace that seems to have a mind of its own. First few years it ran fine then one day it just quit. Started to trouble shoot to find the problem and all of a sudden it started working. Ran great for a few days and it started it again. Not running
In my infinite knowledge I discerned it was either the relay or the limit switch. After an hour drive each way, I purchased replacements. However as I was readying to leave, the furnace came on so I figured I would leave it on and see if it was still running when I returned. To my surprise, it was and did so just fine for a couple of days.
Now it gets weird.
PLEASE correct me if I’m wrong but the way mine works is the Thermostat send a signal to the furnace and a few seconds later the fan starts, at the same time the fan starts a green light comes on on the circuit board. After a few seconds the green light turns red while at the same time the gas comes on and is lit by the spark igniter. It then runs until the thermostat reaches the set temp at which time the gas and the red light shut off at the same time. The fan runs for about a minute (cool down, I assume) and then shuts off
But now the fan comes on with no little green light and runs for about thirty seconds. THEN the green light comes on followed a few seconds later by the red light, gas and spark.
It runs until it reaches set temp and the red light goes off (and I assume the flame too. I haven’t looked) but the fan runs for about 2 2 1/2 minutes and the red light comes back on and we have ignition again. It will run for a while and then the red light and gas go off again. It runs its cool down and shuts off until the thermostat calls for heat again and it starts all over.
What in the world is with this thing?

[enblethen]

Loose connection!
Try removing the cover to the thermostat. Connect the two wires together. The furnace should start immediately and then produce heat. Separate the two wires, the furnace will go into cool down mode and shut off.
The small bi-metal thermostats can act like what is happening. Look at the contacts for pitting. Could use emery board to clean them up. Temporary fix!
A battery powered electronic thermostat is a good replacement.

[87_Alpenlite]

After replacing the relay, it worked fine for about a day and a half. Then again it wouldn't come on. Out of frustration, I hit the wall next to the furnace and low and behold, it came on. the next time it was supposed to come on, it didn't so I smacked the wall again and it came on. This is now the norm. Won't come on, smack the wall, it's on. This is really becoming stressful

[Chris_Bryant]

How old is it? It sounds like it may have a dinosaur board installed, but it could be a fan control or not.
Regardless, part of that sounds like cycling on the limit switch- which could be failing, cutting the voltage to the board down to the threshold of working.

[enblethen]

That does not sound right!
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