Honeywell ST9120C HEAT STAYS ON

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Old 12-31-09, 09:02 PM
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Honeywell ST9120C HEAT STAYS ON

The thermostat sends signal the Mini Zone control module in my closet and LED on the module indicates heat is off. The thermostat does not show flame indicator; however, the heat stays on. I think it might have something to do with the ST9120C board since the AC works fine and same thing happens on both thermostats. How and what should I test to see if a signal is going from the control board in closet to ST9120C to tell it to shut off. My thought is that something is staying energized thus not shutting off the heat.
 

Last edited by sthaas; 12-31-09 at 09:05 PM. Reason: update with additional information
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Old 01-01-10, 01:49 PM
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St9120

Disconnect the zone panel from the furnace. If the heat goes off, the problem is the zone panel.
 
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Old 01-02-10, 10:28 AM
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Looks like there is a small burn mark on the board near the emergency switch. The switch has been broken off. Not good to have clothes up near the board "love where the put it". Anyways, is there a way to bypass the board and wire one zone directly, so that I have heat. I was going to directly connect the thermostat to the wires going from the equipment terminal; however, not sure about the two wires from the zone damper. Any thoughts...
 
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Old 01-02-10, 11:34 AM
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Zone Dampers

I know you don't want to hear this but a zoned warm air system is generally a gross waste of money. That being what it is, let's see what we can do to get you heat.

If no zone is calling for heat, are the dampers open, closed, or some open while others are closed?
 
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Old 01-02-10, 04:33 PM
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Sorry, for the delay... I have no clue and not shure how to check. Was going to assume they all remain open and just direct wire the 4 from thermostat (zone 2) to equipment side. This zone os my upstairs my down stairs has gas fire place and never run heat in the down stairs so not worried about it.


Thank you so much... Again sorry for the delay had an appointment and going to do what I said within the hour.
 
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Old 01-02-10, 04:47 PM
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Maybe a bit of trial & error

No problem on the delay. Seems like a lot of folks are having heater trouble today (usually Saturdays are kind of slow).

I'll try to walk you thru this as best I can without knowing about the dampers but I need to know which wire goes to which terminal on the zone panel. Hopefully, the wires will be red, white, green, & yellow then go to terminals R, W, G, & Y.
 
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Old 01-02-10, 05:25 PM
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You are correct...
The zone also has a red and a white on m4 and m11 the damper...

On the same panel "equipment side" has just r, w, g, and y...
 
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Old 01-02-10, 05:31 PM
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Let's give it a try

Turn off the power to the zone panel & furnace.
Disconnect the stat wires from the panel & hook them to corresponding terminals on the "equipment side" or disconnect both sides & nut the wires together color for color. Let me know when done.
 
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Old 01-02-10, 05:38 PM
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done wired all 4 with wire nuts
 
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Old 01-02-10, 05:44 PM
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Time to test

Restore power to the furnace & panel.
Set the t-stat heat/cool to OFF.
Set t-stat fan switch to ON.
Give it a few seconds (maybe up to a minute) & see if the furnace fan is on AND blowing air thru the vents. If so, switch to HEAT & AUTO & turn the stat up. I'll be waiting.
 
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Old 01-02-10, 05:56 PM
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Restore power to the furnace & panel "DONE"
Set the t-stat heat/cool to OFF. "DONE"
Set t-stat fan switch to ON. "DONE"
Give it a few seconds (maybe up to a minute) & see if the furnace fan is on AND blowing air thru the vents. "DONE"

If so, switch to HEAT & AUTO & turn the stat up. I'll be waiting "I did and flame icon comes on the stat and unit comes on but no flame".
 
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Old 01-02-10, 05:59 PM
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No flame

So we've come 180, from too much heat to no heat?
 
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Old 01-02-10, 06:01 PM
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Yep...
Could having the other zone still connected cause an issue?
 
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Old 01-02-10, 06:04 PM
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Other Zone

Could be. Try disconnecting it. Just be careful not to short any wires to each other or anything metal.
 
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Old 01-02-10, 06:12 PM
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done with same results...
I know the unit is on but no flame and no air flow... But sounds like everything is running...
 
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Old 01-02-10, 06:16 PM
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take that back when the stat shows the flame icon and is set to auto the unit comes on "makes noise" but no flame and the fan is not running. Just tried the same heat but put fan to on vs. auto, get air but no heat "does not ignite" only thing connected to the board now it the 24v transformer and the zone 1 and zone 2 (damper wires red and white)
 
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Old 01-02-10, 06:18 PM
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Something else to try

Go to the furnace & turn off via the service switch. Leave off for 30 - 60 seconds then turn back on. Tell me what happens & when.
Note: Some furnaces upon restoration of power will bring on the fan & exhaust motors for up to a couple of minutes then start their ignition sequence.
 
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Old 01-02-10, 06:30 PM
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More furnace info

Make & model of furnace? Is there some sort of ignition control module & if so make & model, please. Does the model # of the gas valve start with SV?
 
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Old 01-02-10, 06:43 PM
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honeywell ignition 8601U
gas valve honeywell ? do not see model
tempstar see case model number exm36f19c1
 
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Old 01-02-10, 06:52 PM
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8601?

Couldn't find an 8601.
I presume that was a typo & was supposed to be S8610U?

When you break & restore power, what happens? Exhaust blower come on? Any attempt for ignition (sound of spark or pilot lights)?
 
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Old 01-02-10, 07:03 PM
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You are correct on the number...
I turned it off an noticed a small green light come on the ignition box. However went out touched the wire bundle and it came on and system ignited and we have heat. Loose wire in the unit, guess when opening the panels... Anyways will track this down... Tested to see if it would cut off and on like it is suppose too, and it does work quite nice

You said these zoned units are not the best configuration... What is my option with an upstairs and downstairs.
 
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Old 01-02-10, 07:10 PM
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Major $$$

Far & away the best option is a separate system for each floor. Since Tempstar won't let me into their tech section, is that furnace, by any chance, two stage? How about the A/C?
 
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Old 01-02-10, 07:17 PM
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Yes, two stage with AC... Live in Charleston SC, however, always had problems with the heat. Has a tech replace the ignition system last year and worked fine. Each January, brings new issues. I am going to just by another EMM3U and wire it back up. Cheaper then another system for the other zone.
 
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Old 01-02-10, 07:33 PM
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Two Stage

With only 4 wires from the stat, it means you only have a single stage stat & are not getting anywhere near the full benefit from a two stage furnace. Most 2 stage furnaces will go to high fire if the stat is not satisfied in 'x' minutes. Wiring to a 2 stage stat will hold the furnace in low unless the room temp is 2 - 3 degrees below the stat setting. The single stage stat & the furnace going into high fire could cause overheating problems within the furnace especially if only one zone is calling for heat. Time for me to hit the sack. I've been up since 4:15 this morning & have to get up tomorrow by 6:00. Glad things are working well now. Good night.
 
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Old 01-02-10, 08:20 PM
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Thank You! I hope you get a good nights sleep. You saved me from spending money on a tech. here is what I found the board EMM3U needs to be replaced. I also need to replace the wire harness on the ST910C. It "wire harness" has a white connector on either end, and the larger end plugs into the board. When i move it it cuts on and off the little green status light on the ignitor. If you could give me a link where I can purchase this I would appreciate this "just the wire harness". Thank you again...
 
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Old 01-03-10, 01:05 PM
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Wire harness

Slept like a log, thank you.
I doubt you can buy just the wiring harness but I'd bet the end of one wire is not fully seated in the molex connector. If you unplug the harness & while looking into it you can see one wire whose end is not the same length as the others, particularly if you tug gently on each wire. Radio Shack sells wire, the ends, & the tools you need to repair.
 
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Old 01-03-10, 08:27 PM
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Thank you again for the information and the help...
 
  #28  
Old 01-03-10, 09:21 PM
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Where is Ecman? Usually he is FIERCE on checking for poor electrical connections on plugs! He's really missed out on an opportunity to render some of his favorite advice!
 
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Old 05-02-10, 06:13 AM
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I replaced the old board with a HZ322 TrueZone zone control panel and been working great for months. Now I noticed one thing: in the past only one zone would cool or heat at a time. With this new panel it only closes the damper when only a single zone is calling. This was fine during the winter but noticed that my coils and the suction line were frozen 'yes blower working'. I am wondering since two zones are calling at the same time if this is the problem? Second is there a way to have it only cool a single zone at any given time? The unit is 10 years old and I have only cleaned the outside coils several times. Filters changed when they start to look dirty or when they say to be changed.
 
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