DIY Home Improvement Forum banner
1 - 20 of 47 Posts

·
Registered
Gas Furnace
Joined
·
11 Posts
Discussion Starter · #1 ·
Furnace: ICP Model N8MSN090171481

My Guess at the issue: Overheating

Furnace Actions: Starts like normal, runs for a good amount of time (but not consistent) - sometimes days, sometimes 15 minutes. Heat shuts down & blower motor continuously runs. I do have a new sound that was never there before. It sounds as if maybe the bearings are starting to go out on the Inducer Fan Motor. It's not screaming at me yet, but it's definitely a new sound to me.

My actions: Tested continuity in Both Limit Switches (good), tested continuity in Roll Out Switches (good). Doubting myself, I even bypassed the high limit switches individually with no difference in performance. I've removed the duct work with in the furnace, gave it a good cleaning, changed the filter, checked the air return & vents for blockage or closings. I feel like I've done all the 'basic' things that one would suggest.

Question: IF the Inducer is starting to go out, could that be a culprit of the overheating?

Any advice is welcomed; please be kind... :) I am recently a widow trying to make ends meet, but I'm not afraid to dig in and get my hands dirty!

Thanks in advance!!
 

·
Registered
Joined
·
14,687 Posts
That controller can't tell the difference between when a high limit trips or a flame rollout trips. Same diagnostic indicator for both. You'll have to measure the temperature of the supply air. Check the temp of the metal box immediately next to the flame rollout switches.

Don't jumper safely devices.
 

·
Registered
Gas Furnace
Joined
·
11 Posts
Discussion Starter · #8 ·
It appears to be the high limit switch, above the flames, that is the one tripping. The roll out switches have not had to be reset.
 

·
Registered
Joined
·
1,439 Posts
There are limits to DIY problems. It sounds like you have reached those limits. If your furnace is running all day, you definitely need a HVAC tech to check it.
 

·
Registered
Joined
·
16,202 Posts
It appears to be the high limit switch, above the flames, that is the one tripping. The roll out switches have not had to be reset.
The main limit is auto-reset normally, the rollout(s) (are) is manual reset.

If you've had to reset rollout to get the furnace to run, you most likely have a bad heat exchanger though there can be other causes.

How do the flames look? Do they change when the blower comes on?
Do you feel a lot of heat around the burners where the rollouts are? The heat, flame, exhaust should all be getting pulled into the heat exchanger.

The blower assembly can be pulled to visually inspect the heat exchanger.
 

·
Registered
Gas Furnace
Joined
·
11 Posts
Discussion Starter · #12 ·
The main limit is auto-reset normally, the rollout(s) (are) is manual reset.

If you've had to reset rollout to get the furnace to run, you most likely have a bad heat exchanger though there can be other causes.

How do the flames look? Do they change when the blower comes on?
Do you feel a lot of heat around the burners where the rollouts are? The heat, flame, exhaust should all be getting pulled into the heat exchanger.

The blower assembly can be pulled to visually inspect the heat exchanger.
Yes, the rollouts are manual, never had to reset them thus far. The other two limit switches are not manual & do auto reset.
The flames appear fine, they are not 'jumping'.
 

·
Registered
Gas Furnace
Joined
·
11 Posts
Discussion Starter · #14 ·
There are limits to DIY problems. It sounds like you have reached those limits. If your furnace is running all day, you definitely need a HVAC tech to check it.
I have. It was suggested to replace the inducer motor that I was questioning about in my original post. I'm OK with replacing it, I'm just trying to understand as well.
 

·
Registered
Joined
·
16,202 Posts
Yes, the rollouts are manual, never had to reset them thus far. The other two limit switches are not manual & do auto reset.
The flames appear fine, they are not 'jumping'.
If you're sure you've checked every limit on the circuit, check the entire limit circuit. (for voltage drop - leave plugged into board, meter leads into the back of molex connector - if they fit).

Tape blower access switch closed as voltage drop testing has to be done with blower access panel is open but power on.
 

·
Registered
Joined
·
16,202 Posts
I have. It was suggested to replace the inducer motor that I was questioning about in my original post. I'm OK with replacing it, I'm just trying to understand as well.
You can definitely troubleshoot this yourself.

The inducer motor will not cause this - a failing/marginal inducer can cause pressure switches to not close or close be re-open.

Do not change the inducer at this point.
 

·
Registered
Gas Furnace
Joined
·
11 Posts
Discussion Starter · #17 ·
If you're sure you've checked every limit on the circuit, check the entire limit circuit. (for voltage drop - leave plugged into board, meter leads into the back of molex connector - if they fit).

Tape blower access switch closed as voltage drop testing has to be done with blower access panel is open but power on.
Ok. I was wondering if there was a connection going bad in the wiring, molex connector. I can check that. Thank you.
 

·
Registered
Joined
·
16,202 Posts
Ok. I was wondering if there was a connection going bad in the wiring, molex connector. I can check that. Thank you.
If the circuit opens for a while, when it fails you can shut the furnace, disconnect the molex connector and check the loop for continuity/resistance.

With the molex connector on the board - meter leads going into the back of it, you can only go by voltage drop but gives the advantage of testing it live to more easily reproduce it.

At the same time (after checking for voltage drop), you can see if there's voltage between limit circuit and C/common (thermostat wire connection) - checking one side of the loop at a time. (limit circuit has two connections to the board and it monitors the loop)
If there's no voltage on either side, it's probably the connection between the molex connector and board or the board itself - power not
 

·
Registered
Building my last home
Joined
·
3,918 Posts
Do you have the control drawing? If not working on gas appliances with out all of the right tools and meters can be dangerous.

Follow the safety circuit
 

·
Registered
Joined
·
1,439 Posts
You can definitely troubleshoot this yourself.

The inducer motor will not cause this - a failing/marginal inducer can cause pressure switches to not close or close be re-open.

Do not change the inducer at this point.
How can you say that? The HVAC tech was there and you are NOT. Most HVAC service businesses have service warrants, how about you? I can't see why the OP would pay a service call to just get service advice. The OP obviously doesn't know what the problem is and I know you don’t either.
 
1 - 20 of 47 Posts
Top