Thermostat not reaching or maintaining set temp

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Old 02-15-19, 08:42 PM
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Thermostat not reaching or maintaining set temp

I have a brand new furnace but an older Honeywell digital thermostat - model TH4110D1007. The furnace will not reach the set temp on the thermostat or when it does it will not maintain that temp (set to 73 and reading inside temp of 69). Manual shutoff of the furnace and restart shortly after will kickstart it. Removing the thermostat from wall placing back on will also kick start it but it still will not reach set temp. Batteries are new. Nothing is blocking the return air vent. The filter in furnace is new/clean. Switching fan on thermostat from auto to on will turn fan on. Switching system from heat to off to heat will not kick start.
Anyone know the issue or how to fix? Do I just need a new thermostat?
thanks in advance
 
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Old 02-15-19, 09:07 PM
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Welcome to the forums.

Your description is not a thermostat problem. It is a furnace faulting. When you cut power you are resetting the control board. Make and model of furnace is required. Look and see if there is a sight glass in the blower door. If there is.... there will be a flashing LED in there. Count the flashes for a fault.
 
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Old 02-16-19, 07:53 AM
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You’re right - 7 flashes

Lockout due to no ignition. Is that something that I should be able to easily fix on my own or would it require a professional?
 
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Old 02-16-19, 09:19 AM
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I have a brand new furnace
\

Id be on the phone with the installer!
 
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Old 02-16-19, 10:03 AM
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Fault 7 means nothing without at least a make.... and a model number would be helpful.

A lockout code means that a problem occurred at least three times and then the furnace went to lockout.
 
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Old 02-16-19, 11:40 AM
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Lennox

Furnace is a Lennox ML180UH
 
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Old 02-16-19, 01:10 PM
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I couldn't find a 7 fault code in the manual. I left a link below to what should be your manual.
Since the furnace is new.... I'd imagine it's failing on a high heat problem due to not enough airflow.
Your installer needs to check the static duct pressures and the heat rise across the furnace.

You can reset the furnace and watch it as it's working. You should see a code as soon as the furnace fails. The furnace will then do a restart. If it fails in that fashion three times during a call for heat.... it will go into a one hour lockout.

Lennox service manual
 
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Old 02-16-19, 03:28 PM
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Did you install the furnace yourself or did a professional company install it?
Because it should be a no cost warranty for them to come back and fix the problem.
 
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Old 02-16-19, 05:18 PM
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Thanks all. Yes - it was installed by a professional and he is coming back out Monday. Wanted to do as much digging and education as possible first though.
 
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