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Furnace short cycles in early morning, then runs fine

  • Last Updated:
  • Apr 15th, 2019 8:17 pm
Deal Addict
Jun 16, 2009
1708 posts
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Woodbridge
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:
Apr 12th, 2019 10:14 am
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.
With greater power comes greater difficulty in factorizing the polynomial.
[OP]
Deal Addict
Apr 18, 2013
2599 posts
970 upvotes
Canada
newlyborn wrote:
Apr 12th, 2019 11:15 am
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?
Deal Addict
User avatar
Aug 12, 2007
3462 posts
478 upvotes
Waterloo
gbill2004 wrote:
Apr 12th, 2019 9:06 am
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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[OP]
Deal Addict
Apr 18, 2013
2599 posts
970 upvotes
Canada
JivesHVAC wrote:
Apr 8th, 2019 6:23 pm
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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