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Old 10-04-2010, 02:39 PM   #1
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gas furnace short cycle


Had a service last winter where the tech cleaned (scraped) flame sensor??? is what I believe he called it. Furnace still would want to run within 10-15 minutes of previous cycle and our house is tight. Thermostat is a set back, heat/ac and is @15 years old. Does the themostat control this cycling and should it be replaced? It is a Goodman furnace and when installed I don't know if the hi/lo etc. was set up.

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Old 10-04-2010, 03:48 PM   #2
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gas furnace short cycle


some themostats (e.g. honeywell t87f) have an anticipator setting (which can cause short cycling) that can be calibrated to the furnace. it is actually set to the current load wired to it. the default setting is .2 for most applications. i think the variance for most t-stats is +/- 2 degrees. is yours located in a drafty area?

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Old 10-04-2010, 04:33 PM   #3
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gas furnace short cycle


The flame sensor has no control over furnace cycles.

The thermostat, and your homes heat loss determines that.

Has it always done this?
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Old 10-19-2010, 08:03 AM   #4
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gas furnace short cycle


This short cycle has only been noticed after the Goodman furnace was installed with the "old" Chronotherm thermostat. I called a friend in the furnace business who suggested setting the thermostat up 5 degrees. I logged the start of the ignition fan (sorry I don't know the correct name), when the blower started and when the cycle ended. I had a series of @10 minute "cycles" with 2 minutes between cycles where the system was off. The higher fan speed kicked in once in the 5 "cycles" it took to get 5 degrees higher. I remember the old days when the furnace would stay on until the higher setting was satisfied and that is my issue---do these hi-efficiency units cycle on and off until the thermostat is satisfied? Goodman was no help due to liability bla bla bla bla. I felt the repairman jobbed me with the flame sensor cleaning. Heat anticipator sounds like a clue. Thermostat is on an inside wall in the corner of the living room so a draft it not likely. Sorry for the delay in getting back but I have a new grandaughter!!
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Old 10-19-2010, 08:32 AM   #5
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gas furnace short cycle


Replace the thermostat with a GOOD new Honeywell Focus Pro or Vision Pro from HDepot. No el cheapos or you will have more problems. Electronic tstats can go wacky when they get old.
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Old 10-19-2010, 03:47 PM   #6
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You either have a screwed up thermostat. Or a grossly oversized furnace.
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Old 10-19-2010, 04:17 PM   #7
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gas furnace short cycle


it's a old heil gas fired furnace , thermostat is fairly new elctronic type should i try new batteries in it?
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Old 10-19-2010, 04:18 PM   #8
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i have a two level raised ranch house the furnace is a 125,000 btu is that to big for this house? it used to be ok before?
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Old 10-20-2010, 09:24 AM   #9
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Yuri,
Is this a Canadian model?? Home Depot website does not carry either the Focus or Vision. I have Honeywell's model numbers of TH6110D1021 and TH8110U1003. I read the specs and like the random fan for air conditioning to balance the house temp. Thanks.
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Old 10-20-2010, 03:48 PM   #10
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Neither HD not Lowes will have a TH series thermostat.

That is a contractor grade model number.
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Old 10-20-2010, 04:16 PM   #11
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Should be RTH, R for retail. They should have them at the stores and Can Tire sells them too. Store stock can be different than online info.
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Old 10-20-2010, 09:36 PM   #12
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Quote:
Originally Posted by yuri View Post
Replace the thermostat with a GOOD new Honeywell Focus Pro or Vision Pro from HDepot. No el cheapos or you will have more problems. Electronic tstats can go wacky when they get old.
I replaced a ton of those HD stats this past week and none was over two years old.

Been having a boat load of WR good non-programmables go bad too. The room temp reading starts climbing and the furnace short cycles intermittently.
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Old 10-28-2010, 08:46 AM   #13
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Well I called Alpine Products and asked about the Focus or Vision. Now my confusion is do I really need a 3 stage heat, 2 stage cool as the salesman is trying to sell me. He didn't really make it clear as to the benifits of a 3 stage stating the high speed would definitely come on with this unit. It comes on now with my, I think, faulty 20 year old Honeywell Chronotherm. Help please!!
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Old 10-28-2010, 09:20 AM   #14
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gas furnace short cycle


Check how many wires you have connected on the subbase of the tstat and report back here and include a pic. A single stage stat will have RWYG a 2 stage stat will have R W1 W2 Y Y2 G. Doubt if you have a 2 stage stat. All you really need is a 1 stage stat.

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