Fahrenheit 50f head aches

Purchased a floor model Fahrenheit 50f furnace back in 2014. Due to house reno we never had it installed till roughly 2018, done professionally. Unfortunately we've had nothing but bad luck, can't seem to get the air flow correct, no matter what we have a lazy burn. OR will have a great burn but stove will go out after 24 hours of use. Had the tech come back, told us we were doing everything correctly, and keep playing around with the air flow and eventually we would get it. This year we switched pellets types and we seemed to have a nice clean burn with a good flame. That lasted 48 hours. Now we're back to getting a lazy flame and it chucked an error 1 code, lack of vacuum so we're replacing gaskets now. Anyone e
have a Fahrenheit with any success? We have thoroughly cleaned it after each unsuccessful use and at this point it might end up in the yard with a free sign.

Hello
The air in the fire box after it gets heated by the flame, flows up and behind the back firewall down into the exhaust blower and into the venting. This hot air is full of ash and leaves a lot of ash in there. This chamber behind the back wall is only 1/4” to 1/2” deep so it gets clogged up very easily and will make a lazy flame and then go out because the fire can no longer breathe!!
One way to clean that area is to use a 1” piece of metal strapping about 24” to 30” long and stick it into both exhaust ports that go from the bottom of the ash pan all the way up to the heat exchanger (heat tubes.) Another way is to stick the end of a compressor hose in the exhaust ports and blast the ash out with an ash vacuum going to catch as much ash as you can because that can be messy.
It could also be a bad exhaust blower, or bad door or ash pan gasket or stuck sail switch or dirty blocked vent pipe so just check them to make sure.
Hope this helps.

Will give it a try. Thank you!

You're welcome. Let me know how it works out.