I have a approx. 6 year old Carrier 58STA110 natural gas furnace. The blower motor and circuit board was replaced last year. I have installed a new digital thermostat, and the problem is still happening. The filter is new. No return vents are blocked. There is no signal of an error on the furnace LED.

The heating system will call for heat and the system seems to respond appropriately. The blower comes on and heat is pumped into the house. After some time it seems that the whole system suddenly stops. The blower goes off and no gas is being burned. I can hear a small, what I believe sounds like a fan, running inside the unit. I am guessing that is the inducer. Within 30 seconds the gas kicks on and the system runs again. When the system is stopping, the temp in the house is below the target temp.

It seems that the some of the pauses last longer then 30 seconds during the middle of the night. It is very cold outside right now (sub-zero over night). The system is not able to get the temp inside close to the target over night. This has never been a problem before. It is set at 71, but have seen it drop to 64. This has been happening for weeks now, while outside temps were much higher.

Make sure all registers are open.

Make sure air filter is clean.

Make sure the return air is free of obstruction and not blocked.

Post back with results.

I have closed off the registers in our finished basement, as no one goes down there, and the upstairs in in need of the heat the most. All the rest are good.

If the furnace was designed to heat both the house and basement it will over heat if the basement registers are closed. I am just mentioning this since it can be a problem depending upon the design.

Check the setup programing on the new thermostat.

Post brand of thermostst

Post EXACT model of thermostat.

The builder installed the duct work in the basement prior to it being finished. I have opened all of the registers now.

The new thermostat is a Ritetemp 6030. I will remind you that I had the same problem with the previous thermostat, which was the original Carrier brand standard thermostat. I did have issues with that thermostat in the past. The display would turn off, etc. Just before I changed it out, yesterday, it was periodically flashing like it was resetting, and showing "HC." I had never seen that before. So I figured it was finished.

I have the thermostat set to "hold" at 71 degrees now, and set the swing to .25.

My biggest concern it that the furnace is suddenly turning off, then back on. I am not totally convinced that the inability to hold the temp is actually a malfunction. The house is only 6 years old, but when it is -10 outside, I am not sure the system can necessarily keep up. Maybe it should. We have a newborn in the house and I think in the past would have not paid attention to it being cold a few days a year. Like I said, this has been happening for a couple months now, like when it was 50 degrees outside. At about noon today the target was finally reached and it held for a while. It is about 14 degrees outside now.

I should also add that I had begun to use one of these thicker filters, but have since gone back to the cheap thinner filter, as I was concerned that the airflow through the thicker one was being compromised. I did this today. The problem remains.

here is your manual so you have a digital version. Check the jumper install in setup to be sure it matches your system.

http://www.ritetemp-thermostats.com/...tion_guide.pdf

here is rest of info from Rite temp

The RiteTemp Support Site - 6030 Technical Support Page

Lets try this. Lets eliminate the thermostat and see if the furnace run until you turn it off manually.

Unhook the W=white wire from the furnace terminal strip (do not allow it to touch any other terminals or wires) and place a jumper from the W terminal to the R=red terminal. This should keep the furnace running all the time with no shut off. Report back with results. It is also smart to turn off the furnace while making these connections.

Before we do that, I have a change in status here. I now have an error code. I just figured out that the LED resets itself when the system comes back on.

The code is "33," according to the long and short blinks. The sticker on the furnace says this is a "limit circuit fault." It says a whole bunch of other stuff after that if you need it.

It also appears that the gas/burner was turning off and blower still blowing for some time before it all restarted.

The limit circuit fault that you posted is why I already guessed that it was doing and that is why I asked you to make sure all the registers were open. The furnace is telling you that it is producing heat but it is too much heat for the present situation. In other words it cannot get rid of the heat fast enough and the limit circuit fault is a safert control part of the system to prevent furnace damage or possible other problems.

You might read it all then take steps to make corrections. Something like this is on your furnace.

I verified that every register in my house is open. The filter was put in this morning, despite the fact that the "old" one was basically new. The rest of the things to do are above my skill level I guess. Unless I can do the "Flame rollout switch
requires manual reset." But this seems to mean that the furnace did that.

I have a feeling this is a faulty limit switch based on everything else I have read. In fact last night I was in the furnace trying to see if I could reset the manual ones, as the owners manual shows where they are and says to flip them before making a service call. I was not sure if I did it right, as the button you are supposed to push did not feel like a button. The main switch, does not appear to have a button. I really cannot afford to have someone come out here. I already am having to fix the stupid Honeywell humidifier that it attached to this thing. I suspect the solenoid went out on it. Anyway, I think I can do that myself. It is all external and the fix-it kit is only $66.

There is nothing wrong with replacing the switch yourself the bad part is the fact is that in some respects you are replacing it without proof it is really bad.

A partially restricted exhaust pipe or for that matter a combustion air pipe could also cause this. You might check the pipes outside to be sure they are not restricted.

So, maybe I should leave this to a pro, but there is more than one limit switch in the unit. Which one do I replace? The main one, behind the gas valve?

You replace the part that is defective. I cannot tell you which part on your unit is defective from here. Many times people will jump out a part on a TEMPORARY basis to find out which one is defective. It is not recommended that this be done for any length of time or the unit will be running in a very unsafe situation.

There appears to be two switches behind the gas valve. The owners manual identifies this as the main limit switch. How can I find out what the part number for the switch is? Do you know what the part number would be? I think this is it ----- Carrier HH18HA499 Limit Switch. What do you think?

See page 3 for manual reset limit switches location. There is a small button or pin in the center. If pushed it should reset. Save a copy of this on your computer.

http://www.xpedio.carrier.com/idc/gr...t/58st-5pd.pdf

This is not a manual reset limit switch. There is not button or pin. The only limit switches with pins are the roll-out ones.

There are two swtiches spaced a few inches apart that are connected together. My main question is, how do I know what the part number is for these switches?

Unless you can find a parts book OR a web site that converts Exact model numbers to part numbers I have no idea unless you want to actually take the part loose and see what numbers are on it. Many times that info will be right on the part itself. BTW you might call them roll out switches but Carrier calls them manual reset limit switches and the main limit switch is behind the gas valve. Sorry about my confusion with the nomenclature being used.

My Carrier parts info is not on this computer so I can be of no assistance from here. Sorry about that.

One last question. We spoke of jumping out the switch before. On the back of switches these are two wires. If I disconnect the wires and touch them together, is this jumping the switch out? The photo attached is of the switches that I am speaking of. Please tell me if I am way off here.

Leave the jumper wire it is and jump the two single wires together that are on the bottom part of the switches. Remember this is temporary for test purposes so do not run the machine for any length of time. The problem that caused these items to trip is still possibly there and major problems could happen. If for some reason they do not cause the unit to fire when jumped unjump them and test again in that condition. I do not have my wiring diagram for the circuit board in that unit and they could be reverse style limits.