I have a Goodman GMNT High-efficiency Condensing Gas Furnace that is not coming on. It is 5+ years old and had been working fine until the last couple of days. Fortunately, weather is getting better (Spring!), so need for heat is low.

It is a horizontal installation, located in the crawl space under the house. It uses a water ejector pump to get rid of the condensate water. I am assuming that the pump is working, but I don't know for sure. There is no sign of water over-flow near the pump or furnace.

I replaced all the air filters, but no joy. Power is on.

I do not hear the vent fan coming on as it normally does before the burners ignite.

New thermostat installed a few months back is working fine.

Any ideas?

You say the vent motor is on? Do you see a glow from the ignitor?

If the ignitor is not glowing, it could be the ignitor its self or a pressure switch keeping it off. If you take the door off. And the vent motor comes on, and after about 25 seconds you here gas coming into the unit the ignitor is bad. If you do not here any gas the pressure switch is stuck open. There is also a small chance it is the control board not sending power but I will bet it is the ignitor or pressure switch.

The vent motor is NOT coming on... I would normally be able to hear this before the burners lite. But, no vent fan at present.

OK on your t-stat switch it to fan on, and see if the blower comes on. This will tell us if anything at all is working.

OK... the fan works... But, this is the fan that blows air through the duct work.

OK, well lets see then turn it back to auto

When you was in your crawl space did you feel the vent motor to see if it was hot? Also, on that little pump you was talking about there is a main wire on it for electric and probably 2 little blue wires for a safety do you know if the 2 little wires are connected? Also do you have ac on this unit or just heat only?

Fan is back to Auto...

This unit is for both heat and A/C.

The wiring to the condensate pump looked OK to me.

If the safety on the pump is wired to the w turmanal on the control board this would lock out the heat from coming on

I just re-read your question. And, I don't know if the two blue wires on the condensate pump are connect. I would assume so, but I don't know.

And, this unit has been working great for 5+ years.

However, I am wondering if the condensate line is full. From what little I know about the system, the condensate needs to be ejected or it will prevent the combustion fan from operating, which prevents the combustion process from starting.

OK , does your ac come on? If it does then there should be no problems with that little water pump.

So the next step will be to determine if the vent motor has gone bad or if it is not getting power from the control board.

Yes... AC seems to work just fine.

If the condesate is full the vent motor fan will still try to run, but with the extra water in it the pressure switch will not make causing the ignitor to not light. Also on the bottom door with the unit turned to the heat setting. There should be a red flashing light. A fault code this will also tell what may be wrong with the unit.

Sorry it took so long... I had to crawl under the house...

I did not see a flashing light. There is a distinct "buzz", though... an electrical hum. The was from the furnace, not the condensate pump.

The unit is on its side and can not see where the LED might be located and I certainly didn't see anything flashing.

No problem, OK you should have 2 doors on you unit a upper and a lower. The upper one should be larger and contain the vent moror in in the bottom door is just a bit smaller and will have the control board and the blower motor. This door should have a sight glass on it to see the led light. If not you may have to take the doors off the unit.

There is an upper and a lower door. Actually, I would call these access panels since they are screwed to the frame.

In the doors there is a hole in which I can look inside. I did that and did not see any LED lights. In the bottom hole, I can easily see the gas valve.

I do not have access to the top, bottom or back of the unit. So, these two panels are the only ones I can work with. Hopefully, the installers put the unit in so that it could be serviced.