Honeywell RTH9580 thermostat keeps rebooting during heat call


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Old 11-07-14, 04:30 PM
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Honeywell RTH9580 thermostat keeps rebooting during heat call

Any help at all appreciated for a direction to troubleshoot.
I have two of these thermostats, they have both been up since May and I have had no problems with them - until it came time to call for heat. The one upstairs turns on the gas heat, but the thermostat display turns off (powers down and back up)after approximately 4 minutes and comes back after about 53 seconds. I compared the wiring with the one downstairs and they are exactly alike, both have C wire connections and both are connected the same. The one downstairs has been fine.
I called Honeywell and they sent me a replacement, which I installed yesterday (didn't replace the base, just the stat).
I had my fall service today, and the HVAC contractor serviced the furnace and checked everything - didn't find any problems. An hour after he left the replacement started doing the same thing. This seems to be only happening when the stat calls for heat.....
 
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Old 11-07-14, 04:56 PM
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I'd replace the thermostat base.
Post some pics of the wire connections at the stat and at the furnace.
 
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Old 11-07-14, 05:46 PM
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thanks, I was planning on doing that tomorrow.
 
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Old 11-07-14, 05:52 PM
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I suggest you verify you actually have 24V across the R and C terminals on the upstairs thermostat.
 
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Old 11-07-14, 06:04 PM
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Thanks. I did check that and show 24 on my meter.
 
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Old 11-07-14, 06:23 PM
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I should have specified to test the voltage across R and C while calling for heat to see if the voltage drops. I had the same issue with a customer's Honeywell wifi thermostat. It turned out to be a weak transformer. It had a 40VA transformer. We replaced it with a 50VA and the problem was solved. Hopefully the new base will solve your issue.
 

Last edited by firedawgsatx; 11-07-14 at 06:44 PM.
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Old 11-07-14, 06:59 PM
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Interesting. How would you call for heat with only the base on the wall? Not sure how I could do that with no controls. Did you replace the actual transformer on the stat? Thanks for the info. Never had a problem with it all summer while cooling.
 
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Old 11-07-14, 07:09 PM
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Yes, the transformer was replaced. It probably is not the issue in your case. I just threw that info in for informational purposes. FYI: To start up the furnace without a thermostat you can place a jumper wire between the R and W wires at the control board. Adding the G wire starts the blower.
 
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Old 11-08-14, 05:03 AM
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It seems like something is shorting 4 minutes into the heating cycle.

I have seen the white W wire from a Honeywell touch screen stat wired to the C terminal at the furnace cause this as soon as a heating demand was present.

Do you have W2 in use at the stat?
 

Last edited by Houston204; 11-08-14 at 05:54 AM.
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Old 11-08-14, 09:01 AM
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I agree - it seems like something is shorting out. Its very reproducible. I did change the base today and reseated the wires. No change. W2 is not in use.
Attached a pic.
 
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Old 11-08-14, 01:21 PM
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I'm having the exact same issues. In looking over my system, there are some additional wires landed on the 'C' terminal strip in the furnace and I'm wondering if that is causing the issue. In tracing the the wires, it looks like on pair goes to a humidifier, and the other set goes to the A/C.

So on the 'C' terminal I have a blue wire (going to thermostat), a white wire (going to the humidifier), and a red wire (going to the A/C condensing unit).
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Old 11-08-14, 01:30 PM
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If you have the same thermostat it may point to a bad lot of thermostats.

I would bypass the thermostat to help verify the cause.

I would remove power to the furnace and tape off the C wire then twist the R wire to the W wire with a wire nut ( at the stat location). Restore power to see if the problem is still present.

I remember when Carrier had a bad lot of TSTATCCNAC01 digital thermostats back in the 90's that presented these symptoms.
 
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Old 11-12-14, 10:33 AM
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For what it is worth, I have the exact same problem. Same wiring as socrates232. It took almost 10 hours to raise the temp to 72 from 64 because of the constant on and off and the way too early Minnesota chill. Sent an email to Honeywell but don't expect much help here. Might have to go back to my "dumb" thermostat until this is resolved.
 
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Old 11-12-14, 10:59 AM
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Do you have any flash codes on the furnace control board when the thermostat cuts off? It could be that the R wire on the thermostat is losing the 24V at the furnace because of an issue.
 
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Old 11-12-14, 02:49 PM
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Just to update the issue for everyone that helped. HVAC contractor came out today and diagnosed the issue. He checked all the thermostat wiring for any shorts and the circuit board on the furnace for any issues, nothing found. He then was able to catch the issue occurring while monitoring the high limit switch on the furnace. This was what was causing the furnace to kick off. He crawled around the attic and found several dampers that were partially closed which he adjusted. He also checked the return size upstairs and found that undersized along with that duct work. This is a house that is only a few years old that we just bought this spring and the previous owners did 0 maintenance on anything.
Anyway...after all of that said I am going to correct the problems with the return and have the high limit switch replaced to see if that solves the issue. The contractor thinks it should.
 
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Old 11-16-14, 05:31 AM
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Just curious,did this Hi limit open before you changed the Stat?
Geo
 
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Old 11-16-14, 07:48 AM
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Is my furnace too big?

Hi all. I am experiencing the same type of issue. I just bought a Honeywell RTH9580WF thermostat to replace an old simple Honeywell thermostat. My new thermostat is doing the same behavior where it shuts off every ~3 minutes and reboots. Now I have traced it back to the furnace and the thermostat is shutting off when the burners go out on the furnace. I'm assuming the limit switch is getting tripped.

So I can't be certain that this wasn't happening with the old thermostat, it really only came to my attention because the new thermostat was shutting off all the time. The old thermostat ran on batteries so if it was happening back then as well the old thermostat probably quickly sent the signal again to call for heat, so I wouldn't really notice.

Now I'm driving myself crazy trying to figure out why. Could it be my furnace is too big for my house? I have an older Inter-City 125k BTU furnace. 80% efficiency. My house is ~2000 sq. ft. Mainly 1 level but does have a loft. I'm not sure if it matters but I have 14 supply vents. I also have 1 ~12" return trunk that has two "vents" which are about 5 feet from each other in separate rooms.

So could it be my furnace is just too big and tripping the limit switch? Or do I not have a sufficient return? Any help will be greatly appreciated.
 
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Old 11-16-14, 11:17 AM
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Does your furnace have a blinking LED?
What is the model number listed in the nomenclature under the burner panel?
Is the air filter clean?
Inspect the blower wheel and evaporator coil for dirt.
 
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Old 11-16-14, 12:25 PM
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No LED's on my unit. It is a Inter-City NCC5125BKB2. I just cleaned the Filters.
I haven't cleaned my A-coil or blower wheel, it's something I could try.
 
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Old 11-16-14, 01:24 PM
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Geo,

Not sure, this is our first winter in this house and I put up the thermostats after we bought it this May. I haven't made any changes that I listed above yet, but changing the thermostat schedule to keep it from setting back more than a couple degrees seems to have stopped the issue. I'm still waiting on the hvac contractor to come back and replace the high limit switch.
 
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Old 11-16-14, 01:32 PM
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The A-coil wasn't very dirty, but I cleaned it up a bit.
 
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Old 11-16-14, 01:48 PM
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Were you able see the furnace side of the evaporator coil?
 
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Old 11-16-14, 02:31 PM
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Yes. My furnace sits on top of the evaporator coil. I opened up the cover to the coil and the little triangle cover so I could see both parts on the coil. They weren't too dirty but cleaned them up a bit.
 
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Old 01-23-15, 09:34 AM
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Here is what solved this issue for me:
I have a Carrier gas heat furnace, and I even tried installing the new First Alert Onelink (Therm-500) with the same rebooting issue.

I had some techs out to install a humidifier, and look at this issue. They determined that the or one of the high limit switches was tripping and causing this to happen. Very simply they said that the furnace was not getting enough air and causing it to become too hot; in turn tripping the sensor. Furthermore, they said they did NOT think it was a faulty switch. To prove this in a pretty simple way, they removed the filter (Which was a couple of months old, and a 3M Allergen type model to boot.) and ran it without any rebooting! Basically, my filter was not allowing enough air through. I will replace with a new one and see if that works, or if that particular type just doesn't allow enough air through with my furnace setup. (Also explains why in A/C mode, this issue did NOT occur.

Hope this helps one or all!

A
 
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Old 01-23-15, 09:46 AM
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Welcome to the forums.

Some furnaces will interrupt the 24vac to the control board and thus the thermostat power if any of the safety stats are tripped.
 
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Old 02-24-15, 04:16 PM
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Thanks for the additional information.

Looks like we pretty covered most of the bases here. This thread will remain in our searchable archives for future reference.

If you have the same problem and the repair information here doesn't help.... feel free to start a new thread.
 
 

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