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We have a Comfortmaker furnace Model G9MXE0801716A installed…

Customer Question
We have a Comfortmaker...

We have a Comfortmaker furnace Model G9MXE0801716A installed new in May 2015. The furnace keeps shutting off intermittently (mostly during the night when the temperature drops) with Error codes 4 and 7. The technician that installed retired. We called another technician. He replaced the mother board. He's saying that if that does not work (which it didn't) that the furnace is not getting too big for our house? We have all vents open and feels like good air flow. Any thoughts?

Contractor's Assistant: Did you double-check the thermostat's settings? And what about the filters?

We 1st tried taking out air filter and replaced with a new. As far as thermostat - last night was set on 67 degrees and when woke this morning it showed inside temp of 63 and we had LED flashing the error code.

Contractor's Assistant: Do you plan on doing the work yourself?

No. We'll probably call someone - but we were not sure if we should call a different technician since the one who came said he's not familiar with comfortmaker and seems to be grasping for cause.

Contractor's Assistant: Anything else we should know to help you best?

Also - prior to this problem with shutdown and error codes 4 and 7 - last winter we had called the original installer to the house several times to investigate a burning / "hot" smell coming from furnace a couple of times. This also seemed to only occur during the night. (like 1 or 2 a.m.)

Submitted: 8 months ago.Category: HVAC
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Answered in 5 minutes by:
11/21/2017
HVAC Technician: airheatman, HVAC Technician replied 8 months ago
airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 9,215
Experience: Furnace, A/C and heat pump specialist.
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The errors refer to an open limit.If you allow furnace to sit idle for awhile, will it come back on without resetting power or anything?

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HVAC Technician: airheatman, HVAC Technician replied 8 months ago

Below is the diagnostic code and possible causes

LIMIT CIRCUIT FAULT – Indicates the limit, flame rollout is open. Blower will run for 4 min. or until open switch remakes whichever is longer. If open longer than 3 min, code changes to lockout #7. If open less than 3 min. status code #4 continues to flash until blower shuts off. Flame rollout switch requires manual reset. Check for: - Loose blower wheel. - Defective switch or connections. - Dirty filter or restricted duct system. - Improper gas input adjustment - Improper limit switch or no limit gasket.

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Customer reply replied 8 months ago
It will typically come back on. Manual says it will self reset after some period of time. Seems to be good air flow from all vents. Blower working fine. Do I guess we check the other items.
HVAC Technician: airheatman, HVAC Technician replied 8 months ago

I would concentrate first on dirty blower wheel or dirty ac coil if you have ac. The fact that it seems to go into limit lockout on colder nights is an indication that when furnace has to run for longer periods at a time the heat exchanger is over heating.

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