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the annual, my furnace is a POS thread, please help

2K views 20 replies 11 participants last post by  Bones 
#1 ·
furnace has worked flawlessly until today. Replaced the ignitor a few months ago... cleaned the flame sensor then, nd again today, it doesn't seem to help.

Won't stay lit/light. Here is a video of the retardedness



And the fine mo-chine I'm working with. Older Ruud unit.

 
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#2 ·
Usually the flame safety will wait 3 seconds or so to prove flame, it was only like one on your video. I would guess either your gas valve isn't opening right when power is applied to it ( but it sounds like I hear the solenoid clicking open right when the flame starts) or the board isn't timing correctly. Check with a meter and see if you get 24v to the valve right when it opens.
 
#3 ·
I am curious does that model have a Carbon monoxide detector built in above the baffle? last year my buddys 3 year old furnace would start then kick off. he said it would make weird noises then attempt to restart and then kick out after a few failed attempts. he called up the furnace guy who put it in , he came right out. said the baffle burned threw and the thing was defaulting off to keep from generating CO
 
#4 ·
hmmm, it might, wonder what that looks like.

It will try to restart 3 times then just go into bypass until i reset it. About one in 8 times it will actually light though.
 
#5 ·
any chance this thing is a CO sensor? I don't know what else it would do

 
#8 ·
Arrow pointing to what looks like a heat switch....trips if too hot.

Well, not your flame sensor itself....seems to wait far too long between glow and gas. I would do what Tizken said. Check to see when the valve is electrified. Thermostat asks for heat....furnace turns on power vent (mine)....if pressure switch says OK....furnace starts the glow coil.....furnace triggers the gas valve to open.....if flame sensor is detecting flame, gas valve stays open (mine failed 2 years ago)....

It looks like the valve is "sticking"? If thats possible. Do you have the right voltage at the gas valve? Your "door ajar" switch? Too dirty (my dad cleans his out with air every year- he's a heating and cooling guy)?

Side note: Take down your model # of your furnace and get a spare flame sensor, ignitor, and if you can afford it, a gas valve. That saved my ass when I went down wheeling in Tellico for a few days, furnace went out at home, wife called a guy to come over and install the spare ignitor I had, only cost me like 40 bucks.
 
#9 ·
Clean the flame sensor (that thing on the far right burner with the red wire) with some sandpaper. If that doesn't help, that ignition module is probably the culprit. That looks like a delay opening gas valve. The gas comes down the crossover tube, proves flame thru the flame sensor, burners light. All in 2-4 seconds usually. Looks like a Robertshaw module in the pics. All of the safety controls are closed cause you have ignition trial. My moneys on the dirty flame sensor or the fawked ignition module. PM sent.
 
#10 ·
I'm curious why you think the flame sensor would be a problem? When the sensor is in the presence of a flame, it creates a little bit o' volts that the computer reads, if it falls withing a high and low, it passes the flame presence test. That takes at least 5 seconds after the gas valve opens, at least on my furnace..?

It appears that his is failing before the flame sensor comes into play, sure the sensor is probably tripping the failure, but why isn't the gas being triggered earlier?
 
#11 ·
I'd say Curt is right on this one. Usually if it's a flame sensor you will have flame for about 3-5 seconds. In this case, something else is wrong and I bet it's the module. Or that gas valve has a very week coil that is opening tooo late. Check when the gas valve gets power and that it opens right away. Otherwise it's that module.
 
#13 · (Edited)
I checked the voltage on what I would guess is the gas solenoid. It's the big silver block to the right of the arrow (yellow and grey wires). It gets voltage on the first click, no voltage on the second click, imagine that.

The delay between the solenoid opening an closing seems to vary between 1 sec and up to 3 or 4.

edit- how many volts should the flame sensor output? 2-3?
 
#14 ·
Turn off the gas to your furnace. With your meter leads on the gray and yellow wires while they are hooked to the gas valve, you said you get your 24v AC for 3 to 4 seconds. Most trials for ignition are for seven seconds. Unhook the gray and yellow wires from the gas valve and hook your meter terminals directly to them. Cycle the furnace again. If you get 24v for around 7 seconds then your module is probably ok and your gas valve could be the problem. If the 24 volts only lasts 3 to 4 seconds when disconected from the valve then I would lean towards the module. Also make sure that your 24v coming to the module from the thermostat is consistant.
 
#15 ·
well, I forgot to turn off the gas, but I did that...

Even with the gray/yellow wires disconnected, the power is only on for 3 seconds or so. I'm also seeing 18-21V, not 24V, but thats with my el-cheapo voltmeter, so I'm not exactly sure on that one.
 
#16 ·
If I slo-mo the video it looks like the flame never makes it all the way to flame rod, is the crossover tube dirty? I would start by pulling the burners and cleaning them, paying special care to the crossover tube.

The signal from the flame rod is measured in microamps, a cheap meter won't be able to measure it. Basicly the flame rod passes a dc signal back to the module, the flame works as a diode.

Brewchief:d:
 
#20 ·
If by "flame rod" you mean the flame sensor, then yes, the flae does get there, depending when the solenoid kicks off. Sometimes it doesn't get there, sometimes it is there for 2 seconds.

The 24v can vary from furnace to furnace. Is the voltage from w to c (on the the red strip to the left) where the thermostat wires connect always there?
Right now the furnace is running, I'll chack when the furnace kicks off.

Are you still without heat??
The furnace still works one in 10 trys, but it is just a pain to manually reset it after every 3 fails. I have an electronic fireplace, but it doesn't heat the whole house. After 10 hours of no furnace, the house dropped to 55 or so, so not too bad (I only keep it at 62 haha). I do however, need to get this fixed before Tuesday when I leave for vacation, or my pipes will freeze.
 
#21 ·
well, special thanks to Curt. He stopped over and eventually we discovered one of my incoming legs is low, around 100v. That leg just happens to be the one feeding my garage, living room and furnace... all circuits I have had issues with. I switched the breaker for the furnace to the other leg and haven't had a problem (the gas solenoid now gets 23.5V, not 21ish). DTE is supposed to be out late tonight, we'll see what they say.
 
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