HVAC/Furnace help...no warm air coming out of vents..

Just replaced my thermostat thinking that was the problem. Unfortunately the fan still turns on, but no hot/warm air comes out of the vents. The reason I replaced the thermostat was because it wouldn't hold to a certain temp, figured that was the problem, guess not. I checked the breaker box, but nothing tripped (I had to turn off/on for thermostat replacement). I have forced air gas furnace. I have no clue. If I can't get this figured out on my own, I will contact Highclasswhitetrash to see if he can fix it for me, just trying to save some money. Any input is appreciated.

Its a Trane XL80

Make sure there is a call for heat, go downstairs and see if there are any diagnostic lights flashing. They will give a general idea where to start. Report back and I will try to help you here or text message. Don't reset the power switch until you get those codes.

Is it a set-back type thermostat? Many will have a fan on-fan auto switch. How old is the furnace? Is it a standing pilot ignition type? Make sure the access panels are on the furnace and no switches are being bypassed. The fan should not kick-in until chamber is hot. If it's a newer unit it has troubleshooting codes on the bottom panel. Good luck.

as above check for codes. it will have an LED that flashes for instance code 14 is 1 flash pause followed by 4 flashes.

Thanks guys, it is sending me a code, Im working with HCWT now. If I can't get it tonight, Ill get her fixed tomorrow. It sounds like a high limit switch.

HCWT got me set up with a temp fix for tonight. Im all set until he gets here tomorrow. :)

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Originally Posted by TriggerHappy

Thanks guys, it is sending me a code, Im working with HCWT now. If I can't get it tonight, Ill get her fixed tomorrow. It sounds like a high limit switch.

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Someone forgot to change their filter......

Or your blower is dead....

Or your CPU board is dead...
Going through the same shit, been trying to troubleshoot all day.
Induced blower works, ignitor works, circulation blower works, gas valve was randomly working, today nothing happening there, cycling, ignitor glows but no gas igniting.
Going to look for a new board today...

High limits and sticky solenoids on gas valves are very common problems on today's furnaces.

The high limit usually goes bad because of lack of sufficient airflow (clogged or dirty filters) and then your furnace, for a time, cycles off the high limit which will burn it out in a few months.

Would the High Limit burn out gradually or die all at once?
My furnace was working erratically for the last couple of days and then this morning just died...
Are those high limits normally open or normally closed (as in can I jump the wires to test wheter that is the issue)?

They are NC, usually fail open. They are usually intermittent in the failure.

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Originally Posted by MarkCO

They are NC, usually fail open. They are usually intermittent in the failure.

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So, if the issue is the hi-limit and I turn off the main switch and jump the wires bypassing the hi-limit the furnace should work?
I am pretty sure we tried yesterday and still no love.
Then , with the furnace working, it reached the programmed temp, turned itself off and tried again to restart even though theoretically it should have not, but this time although the igniter was glowing, no flame...Weird...That's why I am shooting for the CPU...I have a headache now...

There should be a flashing light and a sheet on the cover that tells you what the light means.

There is a HL, and a flame roll-out, or sometimes referred to as a High-high limit. It is very rare those go out and you should not bypass it.

The simple way to check the high-limit is to put a ohm meter on it. If it shows open, it is bad. If it shows very low, closed, it is good.

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Originally Posted by bellavite1

So, if the issue is the hi-limit and I turn off the main switch and jump the wires bypassing the hi-limit the furnace should work?
I am pretty sure we tried yesterday and still no love.
Then , with the furnace working, it reached the programmed temp, turned itself off and tried again to restart even though theoretically it should have not, but this time although the igniter was glowing, no flame...Weird...That's why I am shooting for the CPU...I have a headache now...

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You need to have someone come out and look at it.

Limit switches don't just go "bad". They go bad by continually being tripped. Boards are not very common to go bad either... The most common problem with boards is the blower relay built into them not turning the blower on.

Limits or any safety should never be bypassed unless for diagnostic purposes only...

I had my board go bad on a unit that was less than 10 years old.

The fan would kick on when it called for heat. Every once in a while I could get the furnace to fire, but then stop after a day or two, sometimes hours. Finally crapped out for good. Everything was cleaned, no LED's lid up. replaced the board with an Ebay new board and worked perfect. Saved $90 an hour on an HVAC guy, and did it all myself. Took the old board off, and when I unplugged from 1 wire, I plugged into other - so I would lose where they went.

GL!

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Originally Posted by fly boy

I had my board go bad on a unit that was less than 10 years old.

The fan would kick on when it called for heat. Every once in a while I could get the furnace to fire, but then stop after a day or two, sometimes hours. Finally crapped out for good. Everything was cleaned, no LED's lid up. replaced the board with an Ebay new board and worked perfect. Saved $90 an hour on an HVAC guy, and did it all myself. Took the old board off, and when I unplugged from 1 wire, I plugged into other - so I would lose where they went.

GL!

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They do go bad.. Just not as often as people (or technicians) think. Its funny to hear from the factory that most of the "bad" boards they get back for warranty aren't bad at all.

The other day I thought I had a board go bad on a commercial water heater. Called tech support and he said "Yup.... sounds like a bad board to me. Board costs $458" . I hang up with him, and I'm about to tell the customer when I find that the fuse had fallen out of the board and it just needed to be put back in.

I had the front cover bowed out a little bit, probably from the last time it was serviced when I was buying the house. It didn't push in the front cover switch enough to tell the unit the front cover was on it.

Just thought I would throw that in there.

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Originally Posted by bryjcom

They do go bad.. Just not as often as people (or technicians) think. Its funny to hear from the factory that most of the "bad" boards they get back for warranty aren't bad at all.

The other day I thought I had a board go bad on a commercial water heater. Called tech support and he said "Yup.... sounds like a bad board to me. Board costs $458" . I hang up with him, and I'm about to tell the customer when I find that the fuse had fallen out of the board and it just needed to be put back in.

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Well, in my case it was the board:
Way too much erratic behaviour, so I got me a board (Do-It-Yourself Plumbing and Heating, $109) and swapped it out.
Came right back on, has been running like a champ ever since.
The annoying part is that this is the 3rd board I change in about 9 years...
Never saw a burn, just a "darker color" around some of the components...
I wonder wether this is just a crappy brand (Goodman) or there is somenthing else causing the boards to fail.
I changed it last time maybe 4 years ago, and the darker color was around different components.
I am going to save this last failed board and compare it with the next.[Bang]

I will trade you a furnace install for that night force... [coffee]

It was a dirty filter, Im pretty sure anyways.