Ok it was time to clean mine so I ran the board test as a refresher.
Step 10 if the switch detects it’s holding a vacuum, the blower will barely start then stop. And keep repeating. As soon as you crack the door open and break vacuum, it will run steady. Close the door and it’s back to pulsing.
Step 11 no RF means the low limit switch is fine, at least for shutting off.
Step 12 the display should show a crude looking “IG”. It takes a couple minutes for the igniter to actually get hot. But if the hi limit is tripped, the display will be blank and the igniter won’t heat up. Your stove lights so that part is fine.
We know something is up with the stove vacuum. You cleaned the exhaust path. I would check and make sure nothing got in the air intake pipe. Small critters, toys, dust balls, etc. Do you have an outside air kit? If so, check that too for obstruction. If you don’t have an outside air kit, see if it runs better when you crack a window. If it runs better, you need one. If all this is good, then the vac switch is probably bad. You can bypass the switch for now to test, but the stove needs actual vacuum to burn right.
Something I’ve had happen before is if it takes a very long time to ignite, the startup mode will time out before it’s hot enough for the low limit to detect that the stove actually lit. Giving the E4 ignite failure. It could be poor pellets, a weak igniter, a weak low limit, or a coated low limit. Oops re reading this I see you cleaned that.
The room blower should not start until the fire is going for a bit. The room blower starts immediately? Not sure if the room blower will start immediately if the low limit is faulty, but you could disconnect the low limit to at least see if that stops immediate starting of the room blower. But the switch would have to be connected to detect that the flame is going. It could be just all out bad.