Hello.. I have a new St.Croix revolution pellet Furnace that was installed the first of October, burning pellets. the unit is hooked to the heat ducts and the return air is connected. This unit ran flawlessly for the first three months running on program 3, heat level 3. During our recent cold snap with temps into the lower teens I bumped up the level to 5, the unit is shutting down due to vacuum issue when running on heat level 4 or 5, by putting a continuity tester across the vacuum switch terminals the needle of the tester is very erratic, based on this I replaced the Vacuum switch, still shutting down. The only way i can keep it running is by closing the draft to 50%, although this is causing a lazy rich burn. Bellow is what I have done to date with no results, I vacuum clean this unit every weekend... New vacuum Switch. Major cleaning of vent pipes, tubes, even pulled the combustion blower, cleaned it, and replaced the blower gasket. Removed the outside air kit then test ran..then hooked it back up...no change. Bumped the draft voltage up...no change. adjusted the burn pot and ash pan doors, no change. If I put a piece of tape blocking the vacuum tube that that protrudes from the side of the furnace, the needle of the tester settles down and the unit will run just fine.. If I pull the front access panel off the unit, the needle of the tester settles down and the unit will run fine. Any ideas? I called St.Croix and of coarse they have not returned my call...my dealer said Vacuum switch...did that. Frustrated in Ohio..