Furnace cycling

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Hi, I've got a forced air propane furnace, Luxaire model GSU082MF Series NAGOE (could be a Q) serial #1310002 Controlled by a Honeywell T87F heat only thermostat. This morning I was down in the basement and noticed that it had the initial ignition then that cut off after a while (normal burn) then a couple of minutes later a second ignition which ran a couple of minutes, when that cut off I headed up the stairs only to hear it kick in a third time for a couple of minutes. Total time for this was about 10 to 13 minutes. Before I went down there I had moved the thermostat only to the point which it kicked in, 60 F from 58 F so, it wasn't that drastic a jump. Yeah, I like it on the cool side. The outside temp was 19 F. I do not remember it ever acting in this manner and suspect there might be a problem, Yes? No? Thanks for any input.
Stone
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pop the cover off the thermostsat and check the ht antcipator setting. <little dial in the center with a pointer on it> set it to .6 and try it again. if this is set wrong it generates heat and fools the stat into thinking the room temp is satisfied.
---------------------------------------------------
Scootz
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3 cycles in 10-13 minutes is to short, you never heat up the unit fully for full efficiency and put extra wear on the unit. Your thermostat should have an anticipator or heat rise setting to allow for longer cycles. I personaly go for the longest cycle till I find the cool down period uncomfortable, giving the most efficiency and least startup-cycle wear. If you have a thermostat manual it will outline settings or someone here will walk you through it. If that doesnt fix it , its repair man time.
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Did the blower come on at any point?
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down
F
and
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Gary Stone wrote:

My guess is the "stack cutoff" sensor is bad. The idea is that shortly after the ignition goes on, the gas should lite and heat up the stack. If it doesn't, the ignition will be killed. But after several tries, it gets warm enough to stay on. Maybe the cold outside temp has something to do with it.
The sensor probably needs to be replaced. It's a safety-related item and the repair should be done by a licensed professional.
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Hi William, hope you are having a nice day
On 11-Mar-05 At About 23:11:13, William W. Plummer wrote to All Subject: Re: Furnace cycling
WWP> Gary Stone wrote:
WWP> My guess is the "stack cutoff" sensor is bad. The idea is that WWP> shortly after the ignition goes on, the gas should lite and heat up WWP> the stack. If it doesn't, the ignition will be killed. But after WWP> several tries, it gets warm enough to stay on. Maybe the cold WWP> outside temp has something to do with it.
This is not the way ignition occurs. the way a pilot is sensed is called flame rectification. the only thing that comes close to what you are saying is the limit switch which has a totally different purpose.
WWP> The sensor probably needs to be replaced. It's a safety-related item WWP> and the repair should be done by a licensed professional.
this is true of any safety device such as the limit.
-=> HvacTech2 <=-
.. "Everywhere is walking distance if you have the time." - s.w.
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Gary Stone wrote:

I'm no expert, but here's my $0.02. Seems like your thermostat has lost the normal hysteresis that prevents this problem. There's a slide-wire heater in the thermostat called an anticipator. Try moving the slide slightly to clean up a poor contact.
Another possibility: did you relocate the 'stat or rearrange furniture such that it is now in a strong airstream from a register?
If all else fails, buy another furnace or move.
Roby
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Ok, I looked at that slider (Heat Anticipator) in the stat and it is set at 5 should I set it higer or lower? Scootz suggested 6.
Stone
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OK, I tried moving it from 5 to 6 (Heat anticipator) and the burner kicked in 4 times during the cycle. Well, I came back upstairs and turned the stat down, didn't want to see if it would kick in again.
Stone
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Hi Scootz, hope you are having a nice day
On 11-Mar-05 At About 22:59:49, Scootz wrote to All Subject: Re: Furnace cycling
S> pop the cover off the thermostsat and check the ht S> antcipator setting. <little dial in the center with a pointer on S> it> set it to .6 and try it again. if this is set wrong it S> generates heat and fools the stat into thinking the room temp is S> satisfied.
If he didn't adjust it previously all this will do is make matters worse.
-=> HvacTech2 <=-
.. "After they make styrofoam, what do they ship it in?" - s.w.
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Thanks Scootz, HvacTech2 is correct, I did try that and it cycled 4 times before I turned the stat down.
Stone
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Hi Gary, hope you are having a nice day
On 12-Mar-05 At About 02:32:47, Gary Stone wrote to Gary Stone Subject: Re: Furnace cycling
>> If he didn't adjust it previously all this will do is make matters >> worse.
>> -=> HvacTech2 <=-
GS> Thanks Scootz, HvacTech2 is correct, I did try that and it cycled 4 GS> times before I turned the stat down.
You have to be careful about following any advice given in a NG as some well meaning people can cause more problems than you had to start with. changing the anticipator could actually burn up the thermostat if done wrong.
-=> HvacTech2 <=-
.. "Sometimes I... No, I don't." - s.w.
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Hi Gary, hope you are having a nice day
On 12-Mar-05 At About 00:00:44, Gary Stone wrote to Gary Stone Subject: Re: Furnace cycling
GS> Ok, I looked at that slider (Heat Anticipator) in the stat and it is GS> set at 5 should I set it higer or lower? Scootz suggested 6.
Don't move it. it is set at a particular point for good control of the temp swing.
-=> HvacTech2 <=-
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Hi, I agree with William and HvacTech2
I had the same kind of problem this fall, and I can tell you that the source of the problem might not be obvious at all for a non professional.
In my case, the problem was at the furnace level. The gas valve was defective and letting too much gas being burned, which made the furnace overheat, and thus the limit switch (I am not sure it is the correct name, it is the dial with 3 tabs) was shutting down the gas burning when the temperature was too high, then the temperature would lower and the switch would let the gas burning resume, and on and on...
Here is a forum with people that are friendly and willing to help you pinpoint the source of your problem, if that is really what you want. I had started a thread (which has diasppeared since then) on my problem back then and I got lots of good info. I called for a tech anyway because I dont like playing in those things, but I do like to understand how things work on the other hand. When I called the techs, I knew that I had an overheating problem.
http://ths.gardenweb.com/forums/hvac /
Good luck!
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You said you moved the anticipator from 5 to 6 and gas cycling increased, did it run complete cylces-fan turning off. You indicated the fan was running, well, why not try moving it to 2. You probably need a pro anyway but it is worth a try
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That would be 4 burns in one cycle, first burn then fan on then burner shuts down and comes back on two to three more times while the fan is running. Whole cycle about 10 to 13 minutes. I could try lowering it as you say. I have put a call in to the local HVAC guy here. Waiting for him to call back. He might be gone for the weekend though.
Stone
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well
changing
To OP: heed the above, I have to ask "Is your filter clean and free of obstructions?"
I know that is obvious but I see it a half dozen times a year...
Joseph

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You know, I did just replaced the filter with one of those pleated ones in lieu of the cheap fiberglass one that was in there about a week ago.
Stone

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One thing you have to remember: You have to change those pleated ones (at least !) every 60 days. Once they get a good "coating" on them, you are going to compromise the effectiveness of your system....
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