My Trane XL 600 (American Standard) furnace is on the fritz. The blower will operate from the thermostat. Jumped R&W @ t-stat and got nothing Jumped @ furnace & got nothing. Fuse is brand new, gas valve is brand new (oof). Standing pilot is lit so thermocouple is good (yes?). I get nothing when t-stat should call for heat. No click and certainly no burner ignition. Could I have a bad (stuck) limit switch? HELP. Forecast is for 24 degrees tonight which is cold in Alabama and I know the tiny ceramic heaters are costing me a small fortune!
Thanks

Make sure the blower door is closed & tight. Also check the gas valve to verify it is set to "on". While we are covering basics, check the emergency & service switches as well as the breaker.

Grady,
Door is closed tight, gas valve is open (pilot is burning) and the switches are on. Any other ideas?

Since the blower operates from t he stat, we can eliminate a transformer problem. An open limit is a possibility but when a limit is open, the fan usually will stay on to "cool" the furnace. With yours being older & standing pilot, that may not be the case. If there is a readable wiring diagram on the furnace, can you take a picture of it & either post here or on a photo sharing site such as photobucket?

Diagram is illegible.

I have checked the limit switches and they all ohm out good (0.002 or less when stone cold) I replaced the thermocouple and re-lit the pilot (because it's inexpensive and humored my father).

So, we have new gas valve, apparently good limit switches, a new t-couple and a lit pilot but no burner ignition. I'm going to try another thermostat that I know to be good to see if that could be the problem.
It's cold in here!

Something super simple I skipped earlier is to verify the gas valve is set to "on" & not "pilot".