Hello all, This is my first post so I apologize for any potential errors in etiquette etc. My Keeprite furnace turns on for a minute or so and then turns off. This repeats about 5 times and then it stays off (no heat is produced). Sometimes after reset, it will work for a day, or two or three but then the problem returns. It's giving me a 3-blink LED code which indicates "PRESSURE SWITCH DID NOT CLOSE OR REOPENED - If LPS open longer than five minutes, inducer shuts of for 15 minutes before retry. If HPS remains open for one minute after gas valve closes (after three successive trials), then furnace control will lockout for three hours before retry. Check for; -Excessive wind -Proper vent sizing -Defective inducer motor -Low Inducer voltage -Defective pressure switch -Inadequate combustion air supply -Disconnected or obstructed pressure tubing -Low inlet gas pressure (if LGPS used) -Restricted Vent -Condensate drainage restricted or blocked If it opens during blower on-delay period, blower will come on for the selected blower off-delay." It works fine when I take the cover off which leads me to believe it's an air supply issue. When this issue began back in the spring I found a bumblebee and some crud in the furnace. I've snaked the line with no improvement. An HVAC buddy of mine has tested all the mechanical/electrical parts and everything is fine. He thought it may be the drainage as the hose was quiet long and led to a "double-trap" situation but we shortened the hose and there's no change. He told me just to take off the pipe so it draws air from the basement and forget about it. I just bought this house and the furnace was installed just last year (by the old owner) and I'd like it to work correctly. The furnace is; Keeprite - NG Model# G9MXE0801716A1 Date of MFG is April 2013 I live in Southern Ontario and purchased this house in May 2014 I appreciate any assistance you guys can provide.

Combustioneer oil furnace, with Beckett burner. Ive become very educated owning this thing. I am goin to make this as short as possible. Primary started triggering last winter. I switched to my propane and said I would addressed this season. First time used this season it worked perfect. When heat was called for the next time it went back to last seasons problem. I havent timed it but it runs the same amount of time every time then trips Id guess 45 seconds. It trips before before the flame goes out. Nice clean burn. I have older CAD cell that I replaced in the past just because of age. Tried it same prob. Measured on unit I disconnected one wire put the ohmmeter between terminal and loose wire before start about goes to M scale and wont even measure , after start 10 k ohm, after trigger about 5 M ohm! This would indicate a bad CAD sensor right? Well when I bench test the CAD sensors I get around 40 ohm in the 12 inches under a 75 watt light bulb and 10 k when covered with thumb. I am assuming the M scale is mega because its capitol M. The CADs are clean, flame is burning clean bright yellowish orange with no smoke coming out of the chimney. I am about to pull my hair out! please advise.