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Old 04-07-2012, 11:08 AM   #1
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furnace gas valve


i have an 11 year old Trane furnace w/ electronic ignition. On a call for heat the induced draft fan runs, the igniter glows but the gas valve doesn't open. No 'woosh'. I checked the roolout, high limit and fan presure switches and they appear good. The circuit board is flashing the correct code. Any suggestions??
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Old 04-07-2012, 11:51 AM   #2
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If your board is not giving you a fault code at this stage then you should carefully check your furnace for any loose ground wires but it is most likely a faulty board. A faulty stat/circuit can also shut down your furnace and leave no fault code. Unlikely, but to test....
Turn off your furnace power/ remove the stat wires R & W from the furnace/ put a jumper between R & W/ turn the power back on to see if the furnace now works when the stat is bypassed.

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Last edited by how; 04-07-2012 at 11:53 AM.
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Old 04-07-2012, 05:38 PM   #3
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While the ignitor is glowing,do you have 24 volts at the gas valve?If no then you have a bad board,if yes then you have a bad gas valve.
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Old 04-07-2012, 08:38 PM   #4
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Hey Rep
I don't understand how he could have a bad valve that the board doesn't detect?
A board that doesn't register a non existant ignition is either faulty, interupted via the stat or suffering from a poor ground.
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Old 04-07-2012, 11:37 PM   #5
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[quote=REP;893944]While the ignitor is glowing,do you have 24 volts at the gas valve?quote]


Agree. Check for 24 v at the gv
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Old 04-07-2012, 11:38 PM   #6
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Yea I went through that too quick.But I also know from experience that a lot of homeowners don't read the flashs correctly.
As long as I'm back on this it could be a vent motor going too slow,a bad pressure switch and a bad board.You could jump out the stat to eliminate that but it does start to cycle so I don't think that.The thing is that it worked for 11 years .You just have to eleiminate each possibility until you get to the fault.
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Old 04-08-2012, 04:25 AM   #7
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His statement about having the right code is a bit vague.
I hear you Rep and agree about the importance of the op reading the diagnostic flash correctly but wouldn't the more certain route be to have him confirm the flash sequence and what his legend says they mean over more complex diagnostic requirements?

His legend is probably..
2 flashes-System lock out.
3 flashes-Pressure switch stuck open or closed.
4 flashes-Open high temperature limit switch.
5 flashes-Flame sensed without gas valve.
6 flashes-115 volt polarity reversed.
7 flashes-Gas valve circuit error.
8 flashes-Low signal at flame sensing rod.
9 Flashes Check igniter circuit and line “N” to 24 VAC Common voltage ( < 2 volts) for a possible grounding problem.

If the light is flashing slowly, everything is working normal and there is no call for heat. If flashing fast, everything is working normal and there is a call from the thermostat for heat.
If the light is continuously lit, the control board is bad and needs to be replaced for the unit to work properly again. If the light is continuously off, check the power source and that the unit is turned on.

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Last edited by how; 04-08-2012 at 01:20 PM.
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