Need gas furnace help

[Slayer0901]

Im working on an amanna gas furnace the problem is sometimes furnace will not light when I get there the only thing running is the inducer fan all pressure switches and limits have always been closed I had a ignition board that is new exactly like the one that is on the unit so I put it on there and told customer we would see how that does,being I never could never get it to do it again 2days later he called and said it was doing it again when I got there he had reset it already so I start working and I was Just removing 24volt tstat wire to reset I have 7.54" wc coming into gas valve I have 3.47"wc going to burners hot surface ignightor is glowing good but would not light I took out gas valve looked in screen I took off burners and orifices nothing is stopped up or have a cobweb or something in it. When it does light flame looks very good alway across and when blower motor comes on flame stays looking good I called fellow tech and he thought maybe crack in heat x but no carbon monoxide at any vents it is natural gas and a 80percent furnace any suggestions would be greatly appreciated thanks

[doc havoc]

First suggestion: Use some punctuation (figured I'd say it first, because inevitably somebody else will)
2nd suggestion: How do you know the ignitor is "glowing good"? Did you amp it or ohm it while cold?

[akelesis]

Is it a hi eff furnace 2 pipe system?

make sure the room has enough combustion air into the furnace room

make sure the vents are clear, there might be a partial blockage in the exhaust pipe.

It could be the inducer motor is over amping not closing the pressure switch. check the pressures at the inducer.

tell the customer when it happens, tell him not to turn off/on the furnace, there should be a fault code displayed on the board. run with that.

Check the drains, see if its plugged clear them as necessary.

I think the board fault will give you a better idea. If you want, call up amana and see if there has been any recent bad parts on that particular unit.

take off the circuit board and see behind it, any signs of a mark or something.

Hope that helps good luck

[Slayer0901]

I ohmed out hot surface ignitor I did not amp it honestly don't know what amp one should be. It is in a crawl space with fresh air vents on all sides of crawl space,I did get on roof and look at exhaust it is clear. It is 80percent furnace with one metal exhaust vent so no drains.i am keeping a constant 27volts on my gas valve so all safety's are closed. I have caught it doing it several times now, just can't figure out with enough gas pressure and an ignition source why it would not light. Is there a way I can make sure the gas and air mixture is correct and I'm not saying it isn't possible but every hot surface ignitor I've seen it has always been either good or bad, but it is getting 114volts

[doc havoc]

What did the ignitor ohm out at? And what type of ignitor? Silicon carbide or one of the nitride? If carbide and over about 90 ohms, I would replace it. Not sure on the nitride ignitors.

[crymtide]

just a small deflection or deformity on the burner the ignitor is in front of can cause an eddy in the gas stream so it only lights sometimes. Have seen it and fixed it a few times. Or maybe even a very slight piece of dirt in the same place. And in my experience it has always been glowing or not glowing as well.

[Slayer0901]

It ohmed out at 52.5

[Flashg21230]

I wonder if the gv even tho it has 24 volts going to it maybe it's not opening all the time.

[Slayer0901]

I caught it while it wasn't lighting and had my manometer on the outlet side going into burners and I had 3.47"wc.

[blitz]

change the igniter. make sure it stays in front of burners. make sure you put the venturi back the way you found it. had a case today on a lennox diplomat that won't lit up. I install the venturi wrong after cleaning and it just won't catch the spark. so I had to take it apart and put it the other way.

[Hvac216]

ive seen that a few times on the goodmans and amanas. its been an ignitor each time. seems rare, but ive had a couple do it.

[doc havoc]

Weak ignitors are more common than some seem to think. However, at 52.5 ohms it sounds like it should be okay. Provided it is a silicon carbide ignitor. If it is the "newer" SiNi ignitor, those numbers are whacked. I believe anything over about 20 ohms on them and they should be replaced.

[19degree]

I had the same issue once, replaced the gas valve and have never been back to customers house for no heat. I was getting 3.4 something wc on original and the new one 3.53 wc