The first thing you must do is ensure that your gas is shut off and disconnected from your tank. Then lift the seat where the heater for a good view of the heater.
Remove the front heater grill that is held on with two screws. And looking in from the front you will see where you can put a couple of small wrenches on and disconnect the gas line. The gas line should easily pull out from the box which will allow everything else in the box to slide forward.
I was able to pull the heat exchanger and circuit board straight out the front after taking the diffuser off the front. The diffuser is held on by two screws. Once you take that off you can undo one screw just underneath the high limit switch and then pull the entire insides of the heater straight out the front. This would be the heat exchanger and the circuitboard that is attached to a metal divider. The internal guts including the fan all just slide straight out but make sure that you are also able to other disconnect your wiring or have enough of it to pull through.
By doing this the whole internal guts of the heater was able to sit on the floor and I was able to put a metre on the sale switch and disconnect the wires off the high limit switch to test that for continuity. I was also Able to check all the connections between the circuit board or any terminals. The unit is quite a simple unit once you look at it out on the floor and there’s not much to it. Circuit boards can be easily found on Amazon for quite a bit cheaper than the dealers. It was difficult to find a high limit switch that is rated at 165° as the original seems to be out of stock everywhere. I spoke to a furnace technician that said if you put in a higher limit by 5° or so it’s not a big deal. I put in 170° High limit switch and it hasn’t
Caused any issues but I’m sure some will argue that as it’s a safety and must be exactly rated at 165. Regardless if you can’t find the parts sometimes you have to put others in that will do the trick. At the end of the day with the issues of my furnace sometimes lighting sometimes not lighting sometimes lighting for a little while and then going out, the whole problem boil down to the igniter that from the day it was from the dealer, it was improperly adjusted and had two large gap. Do your research on the Internet and you will see the gap specifications are Regardless if you can’t find the parts sometimes you have to put others in that will do the trick. At the end of the day with the issues of my furnace sometimes lighting sometimes not lighting sometimes lighting for a little while and then going out, the whole problem boils down to the igniter that from the day it was from the dealer, it was improperly adjusted and had two large gap. Do your research on the Internet and you will see the gap specifications To be 1/8 of an inch. Mine was probably a 16th of an inch more which sometimes didn’t allow it to spark. It was also too far from ground which didn’t allow it to see the flame very well. A lot of furnaces use a thermocouple to make sure that The pilots stay on. What this does is measures between the ground and the igniter a resistance. If there’s no flame it does not see resistance and then shut off the gas valve. The flame contains carbon which allows the igniter to Double as a flame sensor.