# Goodman Furnace Model Number GMNT080-4



## msgbob79 (Dec 6, 2011)

I have Goodman Furnace Model Number GMNT080-4 that quit lighting. I have made checks on it and found that the igniter lights. It cycles on three (3) times and them shuts down. The igniters lights but there is no natural gas flow and it does not fire. In March 2011 I had a similar problem and found that I needed to replace the Gas Valve. After replacing it, I turned the gas on, and set the thermostat so that the furnace would start. The igniter started and then I heard the valve open and then gas flowed to the burners and then the furnace started. I have not had any problems since.

Today I replaced the gas valve again, and found that it does not activate gas flow to the burners. The igniter glows and is working properly. I checked and found that I have 24 volts at the valve. I also found that on the board, there is a red light that flashes 3 times. 

Any help with this problem will be appreciated.


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## hvactech126 (Nov 11, 2010)

your gas valve power is inline with the roll-out switches.... your furnace is KNOWN for heat exchanger failure! Call a PRO to have it examined!!!!!


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## harleyrider (Feb 20, 2007)

If that roll out switch was open the igniter would not glow. MSGbob what is the manifold pressure set at? what is the in-line pressure? these must be measured with a manometer before we can properly diagnose your problem.


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## msgbob79 (Dec 6, 2011)

*In-line Pressure*

I don't have a meter to measure the gas pressure. Will have to call a tech to have it done. Thanks for your post.


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## msgbob79 (Dec 6, 2011)

Don't have a meter to measure the gas pressure. Will have to call a tech in. Thanks for your help.


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## msgbob79 (Dec 6, 2011)

I will call a tech in to have it looked at. I appreciate your assistance. Thanks much. I am just wondering how does a cracked heat exchanger cause the problems that I mentioned in my post?


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## yuri (Nov 29, 2008)

how did U check for 24 volts at the valve. across the 2 wires or from 1 to grd. if across then that is ok and the valve should open. if to grd that is wrong as the rollout is in series with the valve. you can have 24 to the valve and the other line is broken going to the rollout switch and opens the circuit so the valve won't open. if the heat ex is cracked then you get flame rollout.


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## harleyrider (Feb 20, 2007)

yuri said:


> how did U check for 24 volts at the valve. across the 2 wires or from 1 to grd. if across then that is ok and the valve should open. if to grd that is wrong as the roll out is in series with the valve. you can have 24 to the valve and the other line is broken going to the roll out switch and opens the circuit so the valve won't open. if the heat ex is cracked then you get flame roll out.


Yuri, again for the second time in one thread.........if the limit or roll out was open, then the igniter would not energize......he clearly states that igniter is glowing.:furious:


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## hvactech126 (Nov 11, 2010)

harleyrider said:


> Yuri, again for the second time in one thread.........if the limit or roll out was open, then the igniter would not energize......he clearly states that igniter is glowing.:furious:


On that furnace the igniter WILL glow with a roll out tripped! The rollouts are in series with the gas valve power! Calm down Harley!:jester:


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## hvactech126 (Nov 11, 2010)

Now. On to the problem. A three flash is a pressure switch error caused by a blocked vent or failed inducer or a bad switch. Most if the time it is not the switch. Check your flue and heat exchanger.


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## ben's plumbing (Oct 6, 2011)

yes the idea is to help get furnace running not to prove each other wrong. if we make a mistake lets hope our partners can adjust it kindly...we all make mistakes.....i agree with yuri,tech126,and harley...lets get it fixed...:thumbsup: oh almost forgot my 2 cents...check roll out switches.....jump out to see if valve fires...


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## yuri (Nov 29, 2008)

I think I know Harley from B4 aka acefurnacefixer? defunct for awhile and now resurrected but lost it's traffic hvacmech .com? did thousands of posts there back in the day. reminds me of our friend clover. LOL . No problema.:laughing::no:

Goodman does things different than others. most manufacturers put the rollout and limits in series with the circuit board after the tstat energizes. goodman puts it in series with the gas valve just to be different. perfectly safe but adds some wear and tear to the igniter if a limit opens.


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## harleyrider (Feb 20, 2007)

hvactech126 said:


> On that furnace the igniter WILL glow with a roll out tripped! The roll outs are in series with the gas valve power! Calm down Harley!:jester:


I find that hard to buy, but if its true then i will stand corrected and accept my appoligies......I guess given the fact that Goodman (formerly janitrol or as we techs call them junkatrol) is the low baller preferred line I would not be surprised.


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## yuri (Nov 29, 2008)

they do have a cute cost effective ( their specialty ) way of hooking up a 24 volt humidifier that no one else has. no need for a 24 v HUM terminal. just put a pigtail wire on the low fire or main pressure switch and supply 24 volts from there. clever eh.:thumbsup:

5 brownie points for the first correct reply why that works and the reason for doing it.


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## msgbob79 (Dec 6, 2011)

:thumbup: Refer to POST on 12/06/2011 REF: *Goodman Furnace Model Number GMNT080-4*

I had to have a service tech. come and look at my furnace as I did not have any way to check pressure on the lines. After checking he found that the pressure switch was bad. He replaced it and the furnace started right up. Heat again, YES!

This is a simple repair. The repair company chaged me $110.00 for the pressure switch plus labor. I looked on the internet and the switch would cost you under $30.00. If after checking all the components during troubleshooting and nothing is found, change this switch.

The tech told me that the two components that go out on this model of furnace are the pressure switch and the gas valve.


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## Houston204 (Oct 18, 2009)

http://site.famousparts.com/goodman/PDF/IO-213.pdf

I see the rollout switches inline with the gas valve, but it is surprising that the gas valve gets 24 volts without a proven pressure switch.










*Heating Mode*
. The furnace control checks for an open main limit (this
limit is normally closed). If the limit is open, the furnace
will remain inoperable until the limit is closed. During an
open limit, the circulating air blower will be energized. The
status light will blink four (4) times.
. The room thermostat reacts to a demand for heat.
. The control will then check to insure that the vent pressure
switch is open. If, at this point, the vent pressure switch is
closed, the control will blink two (2) times and will remain
inoperable until this situation is corrected.
. The venter blower is energized.
. The vent pressure switch will close when it detects a
pressure in excess of its setting. If the pressure switch
fails to close, the status light will flash three (3) times. The
sequence cannot continue until the pressure switch closes.
. After a pre-purge of about fifteen (15) seconds, the
electronic ignition device will be energized.
. The flame rollout switches are then checked to assure
they are in the closed position.
. After a slight delay, the gas valve will open if the flame
rollout switches are closed.
. The burners will ignite and the flame sensor will detect the
presence of flame. The ignition device will deenergize. If
the sensor does not detect the burner flame, the gas valve
will close and the ignition cycle will be repeated for a total
of three attempts. If, after the third attempt, the presence of
flame is not detected, the furnace will go into a lockout
condition for one (1) hour. It will then repeat the ignition
cycle. This one (1) hour lockout and retry will occur
indefinitely.
. Thirty (30) seconds after the main valve is energized the
circulating air blower will be activated.
. The furnace will remain in operation until the demand for
heat is satisfied.
. Once the demand is satisfied the venter will shut off, and
the circulating air blower will shut off after the field
selectable time off is attained.
. The furnace will remain dormant until the next demand for
heat.​


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