Furnace short cycles after inducer motor replacement


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Old 12-02-18, 06:29 PM
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Question Furnace short cycles after inducer motor replacement

Hi there,

Our 6 year old Gibson furnace had inducer motor replaced last week. Furnace short cycled twice with 4min interval everytime it turned on since inducer motor replacement. This week, it short cycles 5 times with 4min internval and stayed running until scheduled end time. I'm deeply concerned and not sure what's causing it.

Looking for your advise.

Thank you,
 
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Old 12-02-18, 06:47 PM
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A 6 year old furnace should have a control board with a diagnostic LED. See if there's a sight glass thru the blower door. Count the flashes for the fault. The fault code should be on the back of the blower door.
 
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Old 12-02-18, 07:02 PM
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Whats your definition of short cycling? It comes on and off a few times before it stays on?

There will not be a code I would assume unless it locks out..

sounds like an intermittent flame sensor issue possibly?
 
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Old 12-02-18, 07:32 PM
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There should be a fault code before lockout. If it locks out..... reset the power and watch it again.
It almost sounds like it's overheating. Has the filter been serviced/changed recently ?
 

Last edited by PJmax; 12-02-18 at 07:52 PM.
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Old 12-02-18, 08:11 PM
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Originally Posted by lawrosa View Post
Whats your definition of short cycling? It comes on and off a few times before it stays on?

There will not be a code I would assume unless it locks out..

sounds like an intermittent flame sensor issue possibly?
The furnace receives the call for heat, the inducer motor turns on, burners lit, blower turns on, runs for a bit then flames go out, blower runs until the cool down cycle is complete, then it goes right back into the start cycle and does it all again.

Thanks..
 
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Old 12-02-18, 08:44 PM
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does it stay lit eventually and run?

Id have to look up manual but sounds like flame sensor, pressure switch, or yes overheat possibly if fan speed was changed.

Have you called the installer of the fan back?

Yes see if there is a code.. It will help determine issue
 
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Old 12-03-18, 08:35 PM
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No error code. Green and Red lights solid. Solid yellow when flame is on.
Flame lit for about 1.5min and then shuts off. Cool down cycle and then start cycle which does the same as previous post.
Contacted installer and tech came onsite, checked and cleaned drain pipe. Worked for a day and then short cycle again.
 
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Old 12-04-18, 12:06 PM
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Link for video:
https://photos.app.goo.gl/8bjGZxCy3V3X7tXr7

​​​​​​Please use wifi to download or view as files are big size.

Regards
 
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Old 12-04-18, 05:02 PM
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The video was very helpful.

I need the full model number for the furnace. It's on the sidewall near the burner.
I also need the part number on that control board.

It is not a flame sense issue. The yellow LED is only for the flame sense. Locked on yellow when firing is perfect. If you see it flickering...... then it's a flame sense issue.

That control board is not acting normally. Those LED's or at least the red.... should be blinking. That furnace was faulted and the board didn't display it. Since the inducer was replaced..... I'd consider a pressure switch error from loss of vacuum but that would trigger a fault. I'd also consider a gas valve problem but that would trigger a fault. So at the present time..... I'm a little baffled.


Contacted installer and tech came onsite, checked and cleaned drain pipe. Worked for a day and then short cycle again.
The drain line is a condensate line and can affect the pressure (vacuum) to the pressure switch..... but here again..... that should produce a pressure switch open fault.

Ultimately..... it sounds like it's related to the draft inducer and the pressure switch. The technician should come back and immediately put a manometer on the pressure switch line to see if it's out of normal. The furnace may be running on the edge of the correct vacuum due to a leak in the replaced inducer. Possibly a torn gasket.

That draft inducer doesn't sound too healthy either unless it's just the way it recorded.
 
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Old 12-04-18, 07:08 PM
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Hi Pete,
Thanks for the detailed response.
Furnace model#: ​KG7SC038D-23A
Control board part#: Genuine OEM Part # 920915R
Torn gasket: is this also called restrictor plate or gasket. Uploaded picture to same link as video.. If it is, tech didn't install this and said it's not required.
 
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Old 12-04-18, 08:18 PM
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Thanks.... I'll check further.

Typically if a gasket is not used..... some type of silicone is.
 
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Old 12-06-18, 08:41 PM
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Thanks Pete. Looking forward to your findings..
 
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Old 12-09-18, 05:48 PM
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Furnace tech came back and installed orifice gasket. It worked for one day and back to short cycling 3 times now. Not sure what's causing it. ����
 
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Old 12-10-18, 04:41 PM
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No measurements and no diagnostics done. Going to get another furnace company to check this issue.. Very disappointed with this company.
 
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Old 01-30-19, 08:25 PM
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Finally they did pressure measurement and its normal. They contacted Gibson support and told pressure switch may be defective. Is this possible even pressure measurement is good?
 
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Old 01-30-19, 09:00 PM
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The pressure switch has a vacuum level stamped on it where it trips. If the vacuum was confirmed as correct and the switch doesn't close..... that leaves a defective pressure switch.

Pressure switches are rarely defective although it can happen.
 
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Old 01-31-19, 06:00 AM
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Thank you.. I'll update once the switch replaced
 
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Old 01-31-19, 09:37 PM
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Contractor called back and said inducer motor may be defective one and ordered.
Yesterday morning, furnace was unusually short cycled for entire scheduled time. Left the furnace cover open and it was running fine. Noticed inducer motor was hot too.
 
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Old 01-31-19, 09:54 PM
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If the pressure (vacuum) they measured was normal...... then the inducer was fine.
It appears that the vacuum they measured was not high enough.
 
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Old 02-01-19, 11:52 AM
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Replaced inducer motor and pressure switch. Same result.
 
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Old 02-01-19, 11:55 AM
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Vent pipe.. If something blocked along the way, will it cause this issue. Our vent pipe runs for about 35-45ft..

Noticed from yesterday, if the cover left open, it continue to run. If closed, short cycles. Tech checking other possibilities.
 
 

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