I would appreciate any help from online experts as to what they suspect is the issue and how we might go about rectifying it. My furnace guy suspects that there is a problem on the circuitboard where the 24 V circuit will sometimes not allow both the igniter and the gas valve to operate at the same time. Goodman 100,000 btu Model NUG9100FH switched from NG to LP Propane The following parts have been replaced recently: 2 exhaust blowers Gas valve Flame sensor Burner assembly last year My Goodman 100,000 btu Model # NUG9100FH is not firing up properly. It was working fine then we noticed the thermostat would show that the furnace was on the temperature was below or should turn on and when we looked in the bottom window, the Error Code was E0, meaning it was shut off because of excess tries to ignite. I shut off the power then turned it back on in 15 seconds. The furnace will then make up to three tries for the igniter to fire up the burners. If they do not fire in three tries it will shut down again and you have to flip the switch off and on to give it three more tries. One of three scenarios will occur at each try. 1 The low fan will start,the igniter will turn on for a few seconds,the gas valve can be heard opening,but within a few seconds the igniter turns off. 2 The igniter will turn,on the gas valve can be heard opening, and in a couple of seconds it will fire two or three of the closest burners for two seconds, then they will go out and it will shut off again. 3 Igniter will turn on, the gas valve can be heard opening,and all burners will fire with heat beginning and a few seconds the high-speed fan will turn on to drive 100,000 BTU of heat through the burners. There is no consistent pattern in the three scenarios. Sometimes it will fire up immediately (rarely)other times it will go through two number 1’s then a number 2 the next cycle. Sometimes the power has to be turned on and off three or four times (9-12 tries) before it will successfully start up. Once started, the furnace will sometimes run for two hours operating properly through the thermostat yesterday it actually ran for 20 hours on its own before stopping 1° before it should have. Once started today it will only run once and when the thermostat shuts it off it will not restart. So I have been hitting the house to 77° it shuts off, then in three or four hours when the temperature gets down into the 60s I run through the start up cycle again as many times as necessary to start it up

The winter is approaching, I noticed that the furnace in the attic might have problem, here's the symptom: The fan was running while the thermostat was set "heat on" with room temperature lower than the temperature set, the vents kept blowing cool air. Hence the fan didn't stop by itself, so I had to turn the thermostat from heat to off manually to avoid having the fan to run for long time, while no fire was in the furnace I assume. Later I turned the heat back on and things looked normal and the rooms were warmed up. The issue happened several times per week, but I could hardly reproduce the issue when I tried to troubleshoot. I went up to the attic and I saw no error light on the system board(which normally gives an error code), and when I was at the attic to test and monitor, it always worked. I replaced the frame sensor rod with a new one last week, but the issue has happened another 3 times since then. Any idea or suggestion? Also, when I was in the attic and had the top cover removed, I noticed a brownish liquid running(really quickly, just about one second and no more, and I only saw that once, although I believe it could happen often hence we can see the brownish leaking line), please see the attached pictures below, does it indicate another problem? Thank you so much! [img]https://cimg1.ibsrv.net/gimg/www.doityourselft.com-vbulletin/1500x2000/furnace1_a39231abf35f6625263a3ce0508a9366f093d53f.jpg[/img] [img]https://cimg7.ibsrv.net/gimg/www.doityourselft.com-vbulletin/708x839/furnace2_d50bdc3931885a7a47e7c23077e9e281fd5d546e.jpg[/img] [img]https://cimg5.ibsrv.net/gimg/www.doityourselft.com-vbulletin/1500x2000/furnace3_d6998e41611c1d802d9edfe988696e86a6153967.jpg[/img]