I have a Carrier 58GS-050-C-161EA furnace. It was installed back in March of '92 and in the past few weeks I've been having issues. At first it would run fine for a few days, and then shut off. If I cycled the power to the unit it would start again, run fine for a few days and then shut off again. I had a tech check it out and he suspected the pilot assembly was the issue.. . So it was replaced. Two days later, no heat. Another tech visit lead to an adjustment of the pilot pressure.. . 24 hours later same problem. In the past few days there has been a cold snap and the unit has shut off once a day at various times. To date if I cycle the power the unit will start up again - almost immediately.

My understanding is that the t-stat calls for heat, which activates the pilot assembly. When a flame is detected the main valve opens. If no flame is detected the unit goes in to lock out mode and stays there until the power is cycled.. . I think for some reason my furnace is going in to lock out mode.

Here's what's been done so far:

1) Pilot assembly replaced. Jacket on yellow wire was slightly worn and looked to be shorting to the furnace housing. Pilot feed line was also checked for blockages and seemed to be OK.

2) Pilot gas pressure increased to max.

3) I had the supply pressure checked (8 inches of water) and the valve output pressure checked (4 inches of water?) and both were "fine".

4) High limit switch (near chimney) was checked.

5) Tightened loose ground wire on the motor housing.

On Saturday I noticed that there was water dripping from my AC drain line (it's connected to my humidifier drain line). The water was running down around the chimney and on to the terminal assembly (black piece with 5 spade terminals) on top of the valve assembly. I have turned the humidifier off and there is no more water.

Any ideas what the problem might be? My first thought is that the water has corroded something inside the terminal assembly.

I've gone through 2 techs already and still have intermittent issues.. . Yesterday I checked all of the wiring and double checked for myself that the pilot feed line was clean.. . I'm at my wits end and need to get this problem sorted out before the really cold weather hits!

HELP?

Well... no one else has answered and it sounds like you have had a few "pro's" in to check already so I am not sure how much help I can be. However here are some WAGS

a)Intermittent problems are usually electrical in nature. It sounds like you have found and fixed one likely culprit. Perhaps there are others? Not sure about whether the water could have affected anything. If you have a multimeter, you should be able to check for open circuits/ ground faults as you twist and pull various wires. If two 'pro's" have not found an answer, then the problem could be something out of the ordinary.
b) What exactly is included in the pilot light assembly? The other potential is the device that checks for the pilot light flame. It could be faulty, or the flame could be too low. You have done a lot to increase flame height... but have you physically removed the orifice (likely located within an inch or two of the actual flame) and checked for blockages? I just fixed my fireplace by cleaning the orifice of some gummy substance that was blocking it enough to reduce the flame by about 50%.

c) barring that, I think you should just try and watch the operation and perhaps pull/ poke and prod the wires and and hopefully find the set of circumstance that cause failure/ lockout.