My not-very-new Trane gas furnace has been struggling intermittently for many months. It's only gotten really bad about 3 or 4 times.

Here's what it does:

- Quiet clicks I can hear when standing next to it, about 2 per second
- Loud clunking noises about once every 5 or 6 seconds, I can hear it upstairs
- When I look through the vent I see the little blue flame coming on after each clunk, but then it goes off.

- When things are working well, the blue flame is followed by the ignition of the whole bar, red flame.

Sometimes it takes a few minutes to turn on, sometimes a few hours, and a couple times it's gone for a half a day or more. Click, click, click. I've had it serviced twice. No improvement. The furnace repairman suggested I turn on the fan for a while, then switch to auto (for heat). This might have helped a few times, but it's not helping today.

Anybody have suggestions? It's 53 degrees in here! (I'm reluctant to call the same guys whop charged me $120 not to fix it a month ago.)

Don`t blame you for not calling the same guy back, the intermitant problems are the hardest to find . But it sounds like you need someone that is more knowledgeable on Trane furnaces. The next time have them bill you ,then you will have time to see if he does the job right,, a service tech should warranty their work
Turn the power off at the breaker for a few minutes ,sometimes that will help, goodluck

PS,they don`t like to come back a second time for nothing,, maybe it`ll get done right

Without a model number, this is a shot in the dark; what you describe sounds like either 1) a faulty mercury flame sensor, or 2) insufficient gas pressure, causing the gas control's internal pressure switch to open (an often overlooked possibility). If #1 pans out, good luck finding a replacement, as they are no longer manufactured due to the mercury hazard. Look for a cube with a silver capillary plugged into the gas control. The last few times I encountered that situation, I had to resort to a standing pilot conversion.