GMT070-30 furnace lights then after 4 seconds goes off I have replaced the gas valve,flame sensor,igniter,circuit board,and checked the wiring.System worked find last heating season.Please Help:confused:

With all the $$$ you have spent you really should call for ON SITE professional service. The parts you have replaced could have caused the problem but since they have been replaced already you need someone to take a actual look at the unit. All the guess work has been done.

Try replacing the wire from the flame senser to the board. Sounds like a flame senser issue, but since you have replace the actuall senser, it could be the wire( have had this problem numerous times. Good luck, and if this doesn't work, time to call in the pros and watch them scratch their head awhile, or fix it in two minutes.

Thank you for replying,by the way I am a HVAC Serviceman with over 25 years in the business.I was doing everything that Goodman help told me to do but that did not work. I have tried the samethings but it still is not working.

Two stage gas valve?

Four seconds sound about right for high fire during ignition, after wich the second stage(low fire should kick in) is this were you lose flame? Is there a small white switch on the board to switch from one stage to two stage? If there is( and it is set on 2 stage) try switching it to one stage and see if the flame will stay on. Please let me know what you find. I work almost exclusively on goodmans, good furnaces. Also would be helpful to know if the furnace has been converted from nat to lp. I have had this problem only two times, so I am limited on what I can tell you from my hands on experience. Please answer the questions I have asked and I will try to help further.

I do not see a switch on the board.It is a nat.gas furnace,it is about 4-5yrs old.

Is there one or two pressure regulating screws on the gas valve? Did you actually replace the flame sensor or just clean it. I will stick around and try to help you for the next half hour or so, if you want. Just let me know.

One

Did you replace or clean flame senser?

Replaced flame senser already! This one is a tuffy

Would you agree that it sounds like a flame senser problem? Try a new temporary wire from flame senser to board terminal. I know the wire at the board is in a multi connection, but just cut the wire as close to the multi connector as possible(leave enough wire so you can strip and wirenut it back together.

Have you checked inlet and manifold pressure?

Gas pressure inlet is 3.4 W.C.. it sure actted like a bad flame senser,I tried replacing the wire but still the same thing

Are saying wc before valve was 3.4, or after the valve was 3.4,

After

I'm assuming you have two pressure switches, correct? If you do. Turn power of to furnace(door switch will work just fine). Turn power on to furnace, wait till draft inducer starts and then manually suck both pressure switches closed with your mouth, keep sucking on the tubes until ignition and see if you can keep flame this way.

BINGO,the hose has a small crack. THANK YOU for all of your help!! :):):)

Just glad you got her fixed. Sometimes it's the simplist things that will drive you crazy. Take care.


Ps. If replacing the hose does not cure the problem, you have at least narrowed it down to four possible suspects. Bad pressure switch( or swithces) clogged drain lines( if indeed it is a 90 percenter) weak draft inducer, or plugged vent. Please let me know how it all works out.

You should check to make sure that the induced draft motor is keeping a constant vacuum or constant pressure against the air pressure switch. If it doesn't hold enough pressure on the switch, then the gas valve will shut off. Let me know if this helps. Thanks.

If you happen to have a vacuum gauge, it will tell you if your inducer is weak, or you may still have plugged vent or clogged drain lines. If vacuum levels are low, disconnect vent from top of furnace and see if it helps. IF not, disconnect drains from highest point in furnace, if still low vac readings(lower than pressure switch ratings) then you know you have a bad draft inducer.