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Furnace short cycles in early morning, then runs fine

  • Last Updated:
  • Apr 15th, 2019 8:17 pm
Deal Addict
Apr 18, 2013
4313 posts
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Canada
JivesHVAC wrote: I know it might be a pain to do this so early, but if you are able to be awake when the problem arises you'll be able to get the error code (flashing lights in the bottom compartment of the furnace). You can match the error code flashing to the legend to see what's going on. Example 3 flashes = failed ignition or 4 flashes = too many attempted startups. You'll find the error chart on the backside of the bottom cabinet door once removed. Off the bat I'd say dirty flame sensor, but could be other problems. Check what error code you're getting and go from there.
You are just a fountain of knowledge! The short cycling occurred again tonight so I checked the codes as you suggested. According to the legend in the pic below it looks like a dirty flame sensor:
208B1C82-46DF-4BCB-9E3A-7121C4D74BEB.jpeg
Jr. Member
Nov 2, 2015
181 posts
140 upvotes
Oakville
gbill2004 wrote: Is this it?
6986CE3E-C2CE-45E7-9496-4FF71B020E25.jpeg
That would be the culprit, but do note there are other possible issues according to the error code chart. The flame sensor is just the easiest to DIY
Deal Addict
Apr 18, 2013
4313 posts
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JivesHVAC wrote: That would be the culprit, but do note there are other possible issues according to the error code chart. The flame sensor is just the easiest to DIY
True, but the flame sensor seems to be the most likely based on the symptoms i.e. short cycling.

Not sure how I will remove that screw as it does not look like I can use a regular screw driver for that. And I think I will definitely need to remove that white tube to access it.

I'm hesitant to pay a local company to do the cleaning because I'm consider they will find other issues that may not really need to be done. I don't mind paying the $100, I just don't want to be scammed. My GF's brother, who is pretty mechanically proficient might be able to help me with cleaning the heat sensor...

And to the other poster mentioning the secondary heat exchanger being an issue on my furnace, I called Bryant this morning and they said my model number was not affected by the secondary heat exchanger bulletin. They did confirm that both heat exchangers have a 25 year parts warranty.
Deal Addict
Apr 18, 2013
4313 posts
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Canada
Oh and by the way, it did not short cycle this morning, but did short cycle a bit last night, but then got going normally after a couple tries. Seems to be just inconsistent and short cycle periodically.
Deal Fanatic
Dec 5, 2009
5768 posts
3612 upvotes
Have you ruled out the thermostat yet? That should be step 1.
Jr. Member
Nov 2, 2015
181 posts
140 upvotes
Oakville
gbill2004 wrote: True, but the flame sensor seems to be the most likely based on the symptoms i.e. short cycling.

Not sure how I will remove that screw as it does not look like I can use a regular screw driver for that. And I think I will definitely need to remove that white tube to access it.

I'm hesitant to pay a local company to do the cleaning because I'm consider they will find other issues that may not really need to be done. I don't mind paying the $100, I just don't want to be scammed. My GF's brother, who is pretty mechanically proficient might be able to help me with cleaning the heat sensor...

And to the other poster mentioning the secondary heat exchanger being an issue on my furnace, I called Bryant this morning and they said my model number was not affected by the secondary heat exchanger bulletin. They did confirm that both heat exchangers have a 25 year parts warranty.
It's a red hex head screw driver you'll need it looks like. Prob can pick one up for like $3 if you don't have one. Yes remove the white tube if it's easy and doesn't vent to the outdoors. I don't think most companies are out to get a customer and shut their equipment down. That only happens if an actual problem exists and its possibly a matter of life and death.
Deal Addict
Dec 17, 2007
2625 posts
1620 upvotes
Alliston, ON
Does your nest have a C-wire hooked up? It could be the nest trying to cycle the furnace to charge the internal battery. Throw an old thermostat on it for a night and see if you have the same problem. If you do, then dig into the flame sensor. If you don't, then pull in a new thermostat cable so you can use the 5th wire for the C terminal
Deal Addict
Apr 18, 2013
4313 posts
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Canada
fdl wrote: Have you ruled out the thermostat yet? That should be step 1.
Wouldn't the error codes I posted suggest that it is not the thermostat?
Deal Fanatic
Dec 5, 2009
5768 posts
3612 upvotes
gbill2004 wrote: Wouldn't the error codes I posted suggest that it is not the thermostat?
Im not sure but I would just rule that out to be sure. The reason it sounds like a thermostat issue is you had said sometimes it runs fine all day. But in early morning it shorts.
Deal Addict
Apr 18, 2013
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fdl wrote: Im not sure but I would just rule that out to be sure. The reason it sounds like a thermostat issue is you had said sometimes it runs fine all day. But in early morning it shorts.
It's been short cycling in the evenings now as well. I think I'll try and take a stab at cleaning the flame sensor myself and if I can't, I'll hire a company I'm fairly comfortable with who does annual maintenance/tune-up for $100, and as part of that they include cleaning the flame sensor.
Deal Addict
Jun 16, 2009
4517 posts
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Vaughan
Most probably its your secondary heat exchanger plugged. kindly update the thread with real diagnose.
In the meantime, if you pass by your furnace exhaust pipe outside, try to check the easy symptoms
1. Pungent smell from vent
2. Signs of decolorization
gbill2004 wrote: It's been short cycling in the evenings now as well. I think I'll try and take a stab at cleaning the flame sensor myself and if I can't, I'll hire a company I'm fairly comfortable with who does annual maintenance/tune-up for $100, and as part of that they include cleaning the flame sensor.
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Deal Addict
Apr 18, 2013
4313 posts
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Canada
newlyborn wrote: Most probably its your secondary heat exchanger plugged. kindly update the thread with real diagnose.
In the meantime, if you pass by your furnace exhaust pipe outside, try to check the easy symptoms
1. Pungent smell from vent
2. Signs of decolorization
What makes you think the secondary heat exchanger is plugged and not the flame sensor? Can a secondary heat exchanger be unplugged?
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User avatar
Aug 12, 2007
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Waterloo
gbill2004 wrote: Wouldn't the error codes I posted suggest that it is not the thermostat?
I Believe this is what youre looking for.

Image
its only the sensor if the flame actually comes on and you see it thru the (glow) peephole.
Flame not proven = Furnace fired up and open gas valve and powered the igniter but it didn't see a response from the flame sensor indicating that the gas caught fire.

it very well maybe that the gas valve malfunctioned or the igniter didn't fire. So you need to validate that the furnace actually fired.
Last edited by Supahhh on Apr 17th, 2019 5:09 am, edited 1 time in total.
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Deal Addict
Apr 18, 2013
4313 posts
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Canada
JivesHVAC wrote: Good idea. If you kept your old thermostat when replacing to the Nest try to hook it back up to see if the problem persists . If not, new Nest
So the HVAC company come by to look at my furnace. He said it was a crack in a rubber tube/hose in the picture below. He said this is a common cause of short cycling and he sees that or a clogged tube often. In the pic there's 3 black tubes. The cracked one is the one furthest away in the pic. He didn't have a new tube/hose in his truck so he taped it with electrical tape as a temporary fix and he'll try to order me a new tube to replace it another day.

How long could I keep it as is with the electrical tape? The furnace is working like new now.
C1B27367-3CB1-4DA3-A81D-31A80B48DA9E.jpeg

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