# Trane furnace won't ignite



## Doc Holliday (Mar 12, 2011)

Do you hear a click from the gas valve just after the ignitor gets hot?


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## Doc Holliday (Mar 12, 2011)

At this point I'd say the gas valve is failing to open. This could mean that either it's not receiving voltage (but you said you heard a few more clicks just after the ignitor gets hot which is usually the valve receiving voltage) or it's simply gone bad and won't open.


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

have to ask..is gas valve open on line...and is gas valve switch in open position...sorry someone had to ask...ben sr


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## seanarice1 (Oct 24, 2012)

Yes I believe there are 3 clicks after the ignitor gets hot but it doesn't ignite I don't hear the sound of any gas coming out of the burners. I know the gas valve is on going to the furnace and also the main valve is on because it's tied into the water heater which works fine.


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## seanarice1 (Oct 24, 2012)

Here is the gas valve


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## seanarice1 (Oct 24, 2012)

Here is the burners


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## seanarice1 (Oct 24, 2012)

This is the controlboard


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## seanarice1 (Oct 24, 2012)

Model and serial


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## HVACTECH96 (Oct 16, 2012)

remove burners and wash out with water


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## seanarice1 (Oct 24, 2012)

Would that really do anything?


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## seanarice1 (Oct 24, 2012)

I did remove the big pipe feeding the blower there was alot of dust and dirt in there like piles


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## Doc Holliday (Mar 12, 2011)

The ignitor wouldn't glow hot if there was an exhaust air restriction big enough. The order of a furnace on call for heat is exhaust inducer motor starts which pushes air out of that flue pipe, closes a pressure switch which tells the furnace it's okay to light up as the burnt fumes can indeed be removed, then the ignitor glows, then the gas valve is sent voltage and should open, then flames and maybe 20-30 seconds after flames the main blower finally kicks in.

We need to know if indeed the gas valve is receiving voltage. You'd d need an electrical testing meter. Then we need to know both the inlet and outlet gas pressure of the gas valve. Debri in the gas line feeding the furnace can build up and block gas pressure inside the valve.


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## seanarice1 (Oct 24, 2012)

I dont have a voltage meter or know how to use one if I did I bought a new thermostat and hooked it up and still same problem. I assume the gas switch is working because I can feel it vibrate and hear it click while the ignitor is glowing but I could be wrong is there a way to test the gas valve switch to see if it's functioning properly so I can check that off?


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## Doc Holliday (Mar 12, 2011)

A manometer tests pressures. A new digital one comes with fittings you screw into the gas inlet and outlet ports. 

The one I have is around $200.00.


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## Doc Holliday (Mar 12, 2011)

Pretty much if it isn't allowing gas through it's time to change the valve.


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## seanarice1 (Oct 24, 2012)

What are these? There is one on both sides of the burners


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## seanarice1 (Oct 24, 2012)

In the picture above there are two sensors on both sides of the burners I took them out and cleaned them with some steel wool also took out what I believe is the thermocouple which is positioned to be right in the flame and cleaned that reinstalled everything then it fired right up but after about 5min it turned off again and is showering the same problems


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## Doc Holliday (Mar 12, 2011)

Those appear to be some very old flame roll out switches. What those do is sense a high heat situation and on those particular switches the resistors would break, breaking continuity through those wires and shut off the flame while having both the inducer and the main blower motor come on full time, to remove any heat. They are overheating/fire protection switches. 

Newer ones would look like this, can be reset due to the (red) button on top. Yours if ever they tripped would need replacing. The only thing these switches do is sense overheating. If they trip then your furnace would not light up, no glowing of the ignitor at all.


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## Doc Holliday (Mar 12, 2011)

seanarice1 said:


> In the picture above there are two sensors on both sides of the burners I took them out and cleaned them with some steel wool also took out what I believe is the thermocouple which is positioned to be right in the flame and cleaned that reinstalled everything then it fired right up but after about 5min it turned off again and is showering the same problems


I'd try using some steel wool or a scotch brite dish pad on that sensor and upon re-installation making sure all wire connections are tight.


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## Doc Holliday (Mar 12, 2011)

The thing is you didn't do anything when cleaning those roll out switches. And the flame needs to be on for the sensor to work. What the flame sensor does is prove to the control board that indeed flame is on which in turn keeps the gas valve open for continuous flame so the furnace actually has to light up for it to be valid. Your furnace was not even lighting up but now we know at times it's shooting gas. That gas valve is still highly suspect at this time. Sounds clogged to myself.


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## seanarice1 (Oct 24, 2012)

Is there a way to clean the gas valve? It ran most of the night but I woke up to it bring in lockout no surprise there but now it seems to fire up and I hear the gas valve clicking alot and almost shutting off the gas while its burning and then opening all the way and repeating


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## Doc Holliday (Mar 12, 2011)

I've never cleaned one, only replaced them, but I'd suspect removing it completely from the burner and all gas lines, removing all inlet and outlet ports and tapping it/blowing through it to get any and all possible gunk out. 

Before you do that I'd get my hands on a meter and make sure that each time the call for heat is on the valve is indeed receiving a constant 24 volts to open. It very well could be a loose wire connection or if that 24 volts is fluctuating then the problem may lay elsewhere such as in the control board.


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## how (Feb 26, 2011)

Follows Doc's advise for metering the valve's 24Volts while it's operating to determine the cause of the problem.

Do *not* try to open up that valve for cleaning. It's re assembly may well cause a dangerous condition.


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