Comfortmaker furnace not functoning properly

Old 03-28-16, 07:25 PM
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Question Comfortmaker furnace not functoning properly

New blower motor 3 - 4 months old.
Heater had worked well until last night.
Woke up and heater not working.
Thermostat not respond/react to temperature adjustment.
Power down main breaker at least half hour - no change.
So basically no flame/heat and no blower.
Unpluged one contact from limit sensor and a moment later the blower motor kicks on.
Still no heat.
Reconnect limit sensor and turn power on - No heat/fan..
Changed thermostat - no response.
Model specifics: Comfortmaker model ntg3075hfa5 serial L0037 68135
Can't find manual.
What is the most logical sequence to diagnose/fix this?

Last edited by PJmax; 03-28-16 at 09:08 PM. Reason: changed text color -couldn't read
Old 03-28-16, 09:29 PM
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Welcome to the forums.

A colorful post.

Disconnecting a limit wire and having the blower come on is normal. The board thinks the furnace is overheating and is trying to cool it down. I was originally thinking a blown fuse on the blower board but I don't think the blower will run if it's blown.

It can be found on the control board in the blower section. Check it any way.
Down on the same board are the stat connections. Try holding a jumper from R to W and see if the furnace starts then. There is a safety switch on the blower door that will need to be held in for the test.

I was trying to find the service lit. The manual I found shows an intermittent ignition system. That means there is a spark that lights the pilot which lights the burner. Is this what you have ?

Possible manual.... documents/086477/44101260302.pdf
Old 03-29-16, 03:09 AM
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Thank you Pete.
I will check it out when I get some day light.
Mean while I'll have a look at that Doc you referenced.
I appreciate the feedback and will update results later on today.
Old 03-29-16, 08:58 AM
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:HF2: Thank you for the manual it was a good overview.
As of now the system is working to what appears to be normal.
I will put the other thermostat back as I am pretty certain that it had nothing to do with the problem.
As I don't like being in the attic for too long what I did was disconnect all components.
I also noticed the float switch in the catch basin seemed to be at a minimum or negative tolerance so I gave it a slight twist to allow the float to open to what seemed more reasonable and functional.
Once again a big thank you to ~Pete~ for the helpful information.
Oh and as far as jumping the RED and WHITE connections - their is neither on the control board in the unit.
Since I got things working I didn't do it at the thermostat today although I had before my post and there was no effect.
If this occurs again I will be more patient and isolate the culprit.

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