I have a Carrier "Weathermaker" 58SXA gas furnace that has recently starting acting up. I have a programmable thermostat that lets the temperature drop at night to 18 degrees C. In the morning, at 6:15AM, the temperature is set to 21 degrees C. What is happening is that the furnace comes on as it should at 6:15am, runs for about 15 minutes, then shuts off. The temperature has not reached 21 degrees, usually it is still around 19 or so. On the thermostat, it shows "System On", but the furnace is not running. To correct it, I can either flip the switch at the thermostat to Off, then back to Heat, or go down to the furnace and flip the main power switch off then back on. The furnace will start right up, and usually run until the temp is satisfied. It will work great all during the day, and then do this again the following morning. I've cleaned the filter, but that has not helped. There is no lights or sounds coming from the furnace when it is off and the thermostat says "system on".

Anybody have a temperature conversion chart handy? If this is consistent with a long "recovery" cycle coming out of setback, I am inclined to think you have a condensate drain blockage somewhere, and the furnace is flooding before it can complete the cycle & locking out. If I'm right, this will eventually lead to lockout on every cycle. Another possibility: is this a two-stage unit?

18 C = 64 F

Bet it's a second stage unit and the second stage isn't coming on. Would be interested in knowing the outside temp.

Not sure your capable of interrogating the blinks, if it has that abillity. Not sure if it's the Infinity Control either.

Check circuit board for a DIP switch marked LO or LO HT. Turn it on for tonight and see if the problem goes away tomorrow. This would indicate a second stage problem.

18 C = 64 F

Bet it's a second stage unit and the second stage isn't coming on. Would be interested in knowing the outside temp.

Not sure your capable of interrogating the blinks, if it has that abillity. Not sure if it's the Infinity Control either.

Outside temp has been very cold for this area... around -5 degrees C. I'm not sure if this furnace does have a second stage, but it does run for 15 minutes before it cuts out, so shouldn't the second stage cut in earlier than that? I looked at the board for any LED's for blink codes, but I think this unit is too old for that.

Check circuit board for a DIP switch marked LO or LO HT. Turn it on for tonight and see if the problem goes away tomorrow. This would indicate a second stage problem.


I looked at the circuit board, could not find any dip switches at all (also looked at the schematic).

58SXA, eh? I'm workin' with another 58SXA on another thread right now, tune in & chime in...

Looks like "we" got the other 58SXA going-the condensate trap was clogged. Check it out for details.

Looks like "we" got the other 58SXA going-the condensate trap was clogged. Check it out for details.

Yup, saw that in the other post, I've cleaned mine up, and we will see what happens tomorrow morning.

Well, it appears as though cleaning out the trap didn't fix the problem. The furnace still comes on in the morning, runs for about 15 minutes, and then shuts off. It shuts down as if it has reached the thermostat temperature, but it is still about 5 degrees shy, and the thermostat is still on "Heat". I can turn the thermostat off and on, and the furnace starts up again right away, then runs again for about 15 minutes, or less if the temp is satisfied.