Our rental has a concord furnace , the indoor blower runs all of the time , no voltage to the ignitor . I checked all of the limits ,and the all check good. They said when they noticed the problem that the filter was being sucked into the compartment , indicating to me that it was dirty and needed replaced . The LED was flashing a fault of the high temp limit switch. I checked all limits and the operation of the preasure switch , all good .I tried resetting the board but the fault wood not reset. My Idea is to replace the board first. I also checked to see if there was voltage to the ignitor and there wasn't .

Usually the only problem a dirty filter will cause is a trip on high limit. Usually a call to the owner will get someone to fix it. None of my tennants are allowed to work on the furnaces as well as all the other goodies in the homes I own. They usually mess it up worse than when it first broke.