I have a Trane XE80 gas furnace that has been acting similar to others I’ve read about. Everything is working properly in sequence until it gets to energizing the gas valve and delivering gas to the burners. Then after it tries 3 more times, the ignition board displays the 4 flash “Thermal Protection Device Open” signal. When it does finally fire up, after “jiggling” some wires on the board, it will run normal until it decides to mess up again on another start-up sequence.
Since the diagnostic advised that the board was not the problem:
“Open Thermal Protection Device” If the primary (high) limit, auxiliary limit, or rollout limit control opens, the gas valve is de-energized. Both the induced draft blower motor and air circulating motor are energized on low heat speed. The diagnostic light code for this is four short flashes followed by a longer pause. If the primary or auxiliary limit is open, the probable cause is either: low conditioned air flow due to dirty filter or high resistance in duct work, faulty limit, faulty blower, or blower speed set too low. The primary limit will automatically reset, while the auxiliary limit control must be manually reset.
I checked for an internal filter and none were located. I also could not locate any reset buttons on the limit controls (fig.1, fig.2 & fig.3). Even though the diagnostic says it’s not the board, the back of it looks like this (fig.4). When I “jiggle” some of the wires to the board it will cause lots of clicking in the relay and the gas valve will energize and it will either fire up or attempt to. I’ve checked contacts & connecters on the board and they’re clean & tight. I have to leave the front panel off the furnace and have the board lying horizontal on a shelf like shown in the pic or the furnace won’t even attempt to work.
I’m pretty convinced the board is bad but, could it be a combination of things? Also, my kids messed with the numbered dial under the thermostat cover (fig.5). I don’t know what it does, what it should be set at or if it’s adding to the problem. Any advice is appreciated, thanks.