So my apartment has this Trane gas furnace that is giving issues.  It all started with a suspected bad thermocouple.  Sparker would keep going and light pilot light but burners would never turn on.

Replaced the thermocouple and all was well.

Then a day later, it started doing the same thing again.  I started wiggling the wires that run to the gas valve, and it would fire up.

Called maintenance and they replaced the gas valve.... a few hours later the furnace tried to kick on, and the gas valve would turn on for about a second, turn off, turn on, and so on.

Sparker would click, and the pilot light would light, but it just kept doing this and the burner would never light.  

Called maintenance back and they replaced all the wiring harnesses inside the furnace.

Wake up the next morning and hear the gas valve opening and closing again.  Its pretty loud and woke me up.

They came that day and replaced the "sparker box".  I am guessing some sort of transformer that generates the spark to light the pilot.  I think at this point they are stupid because the pilot sparker was working just fine.

Wake up this morning and the damn gas valve is banging on and off again.  Of course the thing works normally and I cant recreate the problem by the time the fix-it guys get here.



The only thing that I can possibly think of that is related is that both yesterday and today when the valve started acting up, the gas water heater kicked on about the same time because my wife was just getting out of the shower in the morning for work.  So my thinking is that the gas valve has some sort of thing where if it opens and there is no flow, or not enough flow, it will turn off.  So possibly the water heater was drawing gas and whatever pressure the furnace was getting was not enough for it to think there was gas.  So maybe an adjustment is needed, but the fix-it guys dont think so, and they want me to call them ASAP day or night (they live on property) so they can come and see the furnace when the gas valve is acting up.



I am getting sick of playing games with these guys, and while I am pretty well versed in home repair, furnaces were never something I really got into.  But if someone can suggest some stuff to try, I can give it a go.

You might call your gas company and have them test the volume and pressure at your house. You might have a bad gas meter, which would mean that there was never anything wrong with your furnace.

I would bet that neither the valve or the harness were bad.
Does the furnace have an inducer (exhaust) motor. If yes, then there is a pressure switch somewhere(in line with the wire to the gas valve).
If the furnace acts up again, jumper accross the swithch and see if the problem quits. If yes, there is a hole in the vaccuum line, a restiction in the vacuum somewhere, or the switch is bad (rare, but possible).
Good luck!

BB

I believe that it is a direct vent type unit.  I went and looked and it appears that it just vents out a stack to the roof.



 

That is an excellent idea.  Now that it is cold they will come on weekends, so that would at least keep the ball rolling over the weekend.



 

I would suspect a bad thermal limiter misreading the temperature in the air handler. Turn the heat off and the fan on and let it run for a little while then see if it will light up and run.

check and clean pilot orifice.should have strong flame to thermocouple,not soft and lazy,check position of thermocouple my not be centered in flame.

take some steel wool and
nd clean the pilot flame sensor there  is no tcouple
on a spark ignition furnace
looks like one but its  not

could be a pilot relight box