Trane XL80 won't heat

I have a Trane XL80 that tries to heat but sometimes fails with a call for heat, but no flame detected. It is not the flame detector as the flame is not there. It turns on the gas, but the ignitor never gets hot. I replaced the ignitor to no avail. I don't want to replace the control board, around $160, without making sure it has to be done. The control board was changed out when the furnace was a little less than two years old by a technecian as it was under warranty. I thought then I might be in for many years of trouble with this furnace... Isn't there a reliable check to verify which part is bad? Can't I repair or improve/modify the board to work more reliably? What do you reccomend?
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On Oct 25, 8:18 am, greynom_at_comcast_dot snipped-for-privacy@foo.com (greynom) wrote:

I don't know that model specifically but I think most of the safety circuits would stop it from turning the gas on if they were preventing it from starting. Somewhere inside it or in the package of paper work that came with it you ought to be able to find a wiring diagram. That would help you determine all the possible things taht may prevent it form starting. Does it have a a fan in the exhaust vent? Is that coming on? Typically most will start the exhaust fan if there is one. Then the ignitor, then the gas. I'm sort of inclined to suspect the control board as well. Particularly since you have replaced the ignitor already. One easy thing to do would e to make sure all the connections form the ignitor to the cotrol board are clean and solidly engaged.
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I have a similiar furnace, the XR80. On mine, the first thing to come on is the inducer fan by the exhaust, then the igniter, then the gas valve opens to ligght the flame, then the blower. By the inducer motor I think there is some kind of safety switch, it's a tube to detect air pressure which senses that the inducer fan is on, otherwise it will shut down. Check if thats clogged or stuck. You say your ignitor was replaced already. To be sure put a meter at the leads and see if it's getting 110V after a few seconds when calling for heat. If it is, then you have a bad ignitor, otherwise, something in the circuitry is telling the ignitor don't come on because of a problem ( for example, maybe because of the inducer safety switch).
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He clams the gas is getting turned on. On just about all models if the pressure switch for the vent fan does not detect that the fan is running it won't turn on the gas.
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wrote:

He clams the gas is getting turned on. On just about all models if the pressure switch for the vent fan does not detect that the fan is running it won't turn on the gas.
I agree. On my Trane (going by memory), the sequence is for the inducer to start; it activates the pressure switch which in turn will turn on the igniter/open the gas valve. If a flame is not detected within a specified time frame the system shuts down and recycle again. If, as the OP says, he is getting gas..and the igniter does not get hot the the problem is somewhere in the circuit that is responsible for providing the power to the igniter. It is also not out of the realm of possibility that the replacement igniter was bad right out of the box. As suggested, measure the voltage at the igniter during the starting sequence. If you get the correct voltage it's obviously a bad (new) igniter. Also, know what voltage to expect...it is not necessarily 110v..mine is around 12v (not 100% sure without looking) MLD
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Last winter heater would run but just cold air. It was a gas valve malfunction. Service replaced and we were good.
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