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Old 01-23-2012, 02:05 PM   #1
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Troubleshooting an intermittent problem (furnace not heating, short cycling)


Hi folks,
1st post here after lots of reading. I'm still troubleshooting and guessing my way through an ongoing issue with my 22 year old furnace.
Started with a "suspected" dirty flame sensor. After cleaning (by a professional) I still had the same issues.

The main issue is: occasionally when the stat is calling for heat, the furnace does not start its cycle

When it is functioning I hear a lot of shorter cycles by the blower. One tech said that it was part of the heat anticipator's settings telling it to do that.
Most of the time when it stops working is in the middle of the night. It has happened a couple times during the day as well.

Usually a reset will get it working for another day or more.
Tech has recently replaced an old controller (?) with a newer White Rodgers that has a g/y/r light that will give error codes.
Each time the house gets cold and it appears the furnace isn't working I check the code and there is NO error. There is also no light signifying its in any sequence of any kind. But there is power to the furnace.

Last tech checked flame sensor, heat exchanger, ignitor, etc. He said all looks good, and tested a lot of the voltage on and around the controller.

I'm stuck. I think its the stat (which is a cheapo Honeywell programmable).
We also got a "low battery" warning on the stat a few weeks ago. Replaced the battery. Could they in any way be a related issue?

Help!


Let me know if there are any questions or pictures you would like me to post to help. Many thanks.

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Old 01-23-2012, 02:49 PM   #2
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Troubleshooting an intermittent problem (furnace not heating, short cycling)


yes, please post a view of furnace with the doors removed, so we can see all of the controls.

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Old 01-23-2012, 04:18 PM   #3
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Troubleshooting an intermittent problem (furnace not heating, short cycling)


Here are a couple of quick pics of my horizontal gas furnace.

The status of the unit when these were taken were the same as what I have been having problems with.
No heat. Calling for heat. No error on the White-Rodgers unit.
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Troubleshooting an intermittent problem (furnace not heating, short cycling)-dscn3324.jpg   Troubleshooting an intermittent problem (furnace not heating, short cycling)-dscn3330.jpg   Troubleshooting an intermittent problem (furnace not heating, short cycling)-dscn3331.jpg  
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Old 01-23-2012, 04:25 PM   #4
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Troubleshooting an intermittent problem (furnace not heating, short cycling)


cleaning a flame sensor doesn't always work, replacing it does.
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Old 01-23-2012, 05:13 PM   #5
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Troubleshooting an intermittent problem (furnace not heating, short cycling)


Good point, Doc.
Something to try.

However, I'm currently setting at no heat. Can't reset.
The cycle isn't even starting when its calling for heat.
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Old 01-23-2012, 05:23 PM   #6
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Troubleshooting an intermittent problem (furnace not heating, short cycling)


nothing at all? No draft inducer motor starting up? I can walk you through a few troubleshoOting steps if you like. May need a few tools such a jumper wire/gator clips, small screwdrivers, even a meter. You got these?

Bypass the thermostat. You do this by removing the cover to expose the wiring terminals. If you have a meter than now would be a gOod time to check for voltage, otherwise you can simply jump R- W for heat, R- Y for cool and R-G for fan on.

If anything works than we know that you have power to this stat. Touch the other terminal first an then bring it to r. Do not let your wire touch anything else, no metal, just the two terminals you are jumping. You can blow a fuse or a transformer if you do. Obviously the R terminal is the power to the stat from the furnace. If you do not have power at all, if nothing comes on, let us know.

Either way, let us know.
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Last edited by Doc Holliday; 01-23-2012 at 05:33 PM.
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Old 01-23-2012, 05:43 PM   #7
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Troubleshooting an intermittent problem (furnace not heating, short cycling)


If you have "low battery" that maybe the main problem. But I also will check for good ground because that board needs 100% good ground. I had replace 4 of them this year over poor ground.
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Old 01-23-2012, 05:49 PM   #8
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Troubleshooting an intermittent problem (furnace not heating, short cycling)


Looks like it has a TDR (timed delay relay) to bring on the id motor......next time its locked up see if the relay is getting and sending power to the ID motor,.......that would be the first thing i would check.
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Old 01-23-2012, 05:55 PM   #9
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Troubleshooting an intermittent problem (furnace not heating, short cycling)


By looking at that pic were high voltage is coming in I see no ground wire. Only from control board to furnace metal box. Yes some time bx cable can be used for ground but not 100% ground. Run ground wire or get someone to run it
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Old 01-23-2012, 06:16 PM   #10
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Troubleshooting an intermittent problem (furnace not heating, short cycling)


Quote:
Originally Posted by Tator1076 View Post
By looking at that pic were high voltage is coming in I see no ground wire. Only from control board to furnace metal box. Yes some time bx cable can be used for ground but not 100% ground. Run ground wire or get someone to run it
Look a little further down......the top wires are for the inducer motor from the TDR i mentioned earlier....
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Old 01-23-2012, 08:53 PM   #11
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Troubleshooting an intermittent problem (furnace not heating, short cycling)


Quote:
Originally Posted by Tator1076 View Post
If you have "low battery" that maybe the main problem. But I also will check for good ground because that board needs 100% good ground. I had replace 4 of them this year over poor ground.
The low battery issue was a few weeks ago.

Again, I was able to reset many times until this afternoon.

I will be trying a few things out tomorrow.
Thanks for all the help so far.

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