Fresh air blocked or not?

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GMM

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For the past couple of winters, my furnace goes through a period of stopping, particularly during the coldest days of the season. The service technician replaced the logic board during one of his visits, but that did not stop the problem. I checked the fresh air intake, and there was nothing blocking it. However, the furnace would start when I disconnected it as it pulled air from my two-car garage where the furnace is located. When the weather improved, the furnace would run without any problem. Is this a sign that my 13 year old high-efficiency furnace needs to be replaced, or is there something about my furnace that cannot deal with very cold air? Thanks.
 

Stuff

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What was the code displayed? Were you able to re-create the problem when the tech was there? Possibilities include a bad pressure switch. Maybe even a weak inducer motor but most likely still a pipe problem. On coldest days frost can build up and block the intake. Did you check the exhaust vent as well?
 

GMM

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What was the code displayed? Were you able to re-create the problem when the tech was there? Possibilities include a bad pressure switch. Maybe even a weak inducer motor but most likely still a pipe problem. On coldest days frost can build up and block the intake. Did you check the exhaust vent as well?

Unfortunately, the technician didn't share the code. I watched him troubleshoot the furnace, and he was able to re-create the problem. He replaced the logic board, and it worked for the rest of the season; but, the problem happened again last winter. I don't recall if he tried to re-create the problem after the new logic board was replaced (note to self ....). If the problem goes away when the garage air is used, I guess there is something about the pipe or how the air is getting into the furnace. I like your ideas about a bad pressure switch or a weak inducer motor. Could you explain how a bad pressure switch or a weak inducer motor would cause a problem? I'll check the exhaust pipe, too. I would think that if that were the problem, it wouldn't matter if the furnace was drawing air from outdoors or from in the garage. But, I'll still check it out. Thanks for your help.
 

Jadnashua

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When the unit is closed combustion (i.e., one where it has dedicated duct - often pipe for air supply and exhaust), there is almost always some sort of pressure/vacuum sensor(s) to determine if either the incoming air supply or the exhaust is partially blocked. Note, this can also be an issue if the effective length of those ducts is too great. This is the 'effective' length, which accounts for things like grills, elbows, in addition to the actual length of the pipes/ducts involved. There are often numerous interlocks in the system, and they all need to be working properly AND the installation needs to be within specs.

When they installed my current boiler, the guys ignored the instructions and reversed the intake/exhaust at the grill...this caused condensation to dribble down onto the intake and on a really cold day, eventually shut the boiler down. If yours is also a condensing unit, the pipes must be properly sloped and the condensate must be plumbed properly or it can create issues as well. Often, the theory of operation section of the manual may give you some insight on what is required to make things work, and the troubleshooting section can help as well.
 

Jadnashua

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When the unit is closed combustion (i.e., one where it has dedicated duct - often pipe for air supply and exhaust), there is almost always some sort of pressure/vacuum sensor(s) to determine if either the incoming air supply or the exhaust is partially blocked. Note, this can also be an issue if the effective length of those ducts is too great. This is the 'effective' length, which accounts for things like grills, elbows, in addition to the actual length of the pipes/ducts involved. There are often numerous interlocks in the system, and they all need to be working properly AND the installation needs to be within specs.

When they installed my current boiler, the guys ignored the instructions and reversed the intake/exhaust at the grill...this caused condensation to dribble down onto the intake and on a really cold day, eventually shut the boiler down. If yours is also a condensing unit, the pipes must be properly sloped and the condensate must be plumbed properly or it can create issues as well. Often, the theory of operation section of the manual may give you some insight on what is required to make things work, and the troubleshooting section can help as well.
 

GMM

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When the unit is closed combustion (i.e., one where it has dedicated duct - often pipe for air supply and exhaust), there is almost always some sort of pressure/vacuum sensor(s) to determine if either the incoming air supply or the exhaust is partially blocked. Note, this can also be an issue if the effective length of those ducts is too great. This is the 'effective' length, which accounts for things like grills, elbows, in addition to the actual length of the pipes/ducts involved. There are often numerous interlocks in the system, and they all need to be working properly AND the installation needs to be within specs.

When they installed my current boiler, the guys ignored the instructions and reversed the intake/exhaust at the grill...this caused condensation to dribble down onto the intake and on a really cold day, eventually shut the boiler down. If yours is also a condensing unit, the pipes must be properly sloped and the condensate must be plumbed properly or it can create issues as well. Often, the theory of operation section of the manual may give you some insight on what is required to make things work, and the troubleshooting section can help as well.

Thanks for your reply. The furnace ran without a problem for the first 10 years, so I'm don't think its the length of duct or the elbows, but I will take up the issue with the next technician. Maybe the duct work put stress on the furnace which lead to the development of the problem.
 

Dana

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A mouse nest or build up of debris in the combustion air intake duct could lead to those sorts of symptoms developing over time, especially if the total equivalent-length of the duct run was more than half the max allowed in the installation manual.
 
J

jameshenry12

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This is the defect of condenser. It will be better if you show this to qualified electrician rather than roadside electrician.
 
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