Day & Night won't ignite

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Old 12-18-08, 03:11 PM
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Question Day & Night won't ignite

I have a Day & Night model 100HCU-12B, series 652 forced air furnace. We recently removed the furnace filter to be changed to begin the winter season. While the old filter was absent we ran the furnace and it seemed to fire up and work fine. After replacing the old filter with a clean one the furnace will no longer ignite. The pilot is burning but it will not fire up. Neither the blower or burners are working. I am trying to fix it myself but I am puzzled. Any help with this would be greatly appreciated and please be very basic as I am a novice at this. Thank You
 
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Old 12-18-08, 03:45 PM
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Is this scenario occuring NOW?: Where you leave filter out and it works, and put it back in and it quits? If you think it is, be sure to do several tests each way to rule out coincidence.
 
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Old 12-18-08, 08:37 PM
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I have tested it and it doesn't seem to have anything to do with the filter.
 
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Old 12-19-08, 08:16 AM
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So the bottom line is - you can't figure out why you can have a working pilot and yet it won't fire up?

Is this pilot lit automatically when there is a call for heat, or is this a standing pilot, as this answer can greatly matter as to know if an ignition sequence is trying to start.

If yours automatically ignites, upon a call for heat, yet does not continue the whole ignition process, depending on your furnace type, maybe you have a flame sensor for the pilot that will allow the pilot to remain lit but wil not let the burners come on unless the flame sensor can sense the pilot flame.

The pilot flame may be low due to a partialy clogged orifice or a dirty flame sensor for the pilot (not the flame sense for the burners). Or, depending on your type, if you have no speciifc probe-type pilot flame sensor for the pilot, then the pilot assembly itself senses the flame. In either case, removal of the pilot assembly may be necessary to clean out the piliot and polish up metal down there that the pilot flame contacts.

If you hear a gas valve click, AFTER the pilot is already on, or have checked for MV (main valve) voltage at the gas valve and you get the 24 voltage, then the paragraph just above would not apply. (It would not apply because that means that the pilot flame sense is working, the control module or board has acknowledged it, and it is allowing the firing sequence to progress to at least TRYING to open the main gas vlave to the burners.)

Grady often suggests a simple test. When the pilot comes on, you should try to hold one of those barbeque lighters into the burners to see if the furnace fires up. That way you would know if the gas valve is opening.

But I will presume that it is not. Then we need to know if the gas valve clicks after the pilot has lit. If so (only), you could try to rap on the gas valve with the butt of a screwdriver to see if you jar the valve open.
 
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Old 12-19-08, 12:55 PM
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Is there a door switch behind the blower assembly door, presumably that is where you replaced the filter.
 
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Old 12-19-08, 03:22 PM
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It is a standing pilot and there is absolutely no sound whatsoever. Just the lit pilot. No clicks, no switches in the blower housing, and a very basic pilot dial. Here is a picture index I don't even think there is a pilot setting.
 
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Old 12-19-08, 04:01 PM
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Can you please answer post #5? To get timely help, one really needs to answer questions. That was a good question because there is a safety switch on blower doors that completely shuts off the furnace, so the blower cannot come on, nor the burners. If that cover was not put on correctly, or left off, the furnace will not run. It will simulate a blown fuse or tripped circuit breaker, furnace switch turned off, inoperable thermostat, broken thermostat wire, bad connections, etc.

If you answer #5 (and possibly check things mentioned in the last 3 lines of pararaph above), then we can move on.
 
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Old 12-19-08, 06:17 PM
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the picture appears to be a Tafco valve and it uses a flame switch not thermocouple type pilot. It is difficult to be 100% sure, due to the picture position. Is the pilot clean, meaning not burning yellow. The pilot if it is a flame switch must be clean to allow the bi-metal portion to warp into position.
There would be no door switch on a model this old.
 
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Old 12-19-08, 10:00 PM
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It does seem to be burning a little yellow (not blue). How would I go about cleaning the pilot? Should it be removed? Or is there some other way to clean it? Here is a picture of the pilot
 
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Old 12-19-08, 10:34 PM
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Another try at posting the pilot picture index
 
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Old 12-20-08, 03:29 PM
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Originally Posted by starsky1138 View Post
Another try at posting the pilot picture index
Yes that is the flame switch I mentioned earlier. I can see by the picture it is quite dirty and I suspect cleaning will result in a cure. I guess the best way you could clean is: turn off gas and blow air thru the top where the flame comes out. You may have to actually remove and disassemble if the first attempt doesn't result in a blue flame. If you need to disassemble also turn off the power to furnace.
To disassemble remove pilot tubing and the orifice should fall out. Don't lose the orifice. Look inside where the orifice was and you will see a bunch of lint or maybe even a fly or spider nest. Do you have an air compressor or a can of air to use?
 
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Old 12-21-08, 12:12 PM
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I cleaned the pilot. I even removed it to clean it. I scraped it off because there were deposits on it. I even cleaned out the cabinet, still nothing. Is it a possibility that the burners are not getting the signal from the thermostat? How would I go about testing this? I have a Radio Shack 22-221 multimeter just let me know the settings and I could check that out. Thank You
 
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Old 12-21-08, 04:52 PM
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Originally Posted by starsky1138 View Post
I cleaned the pilot. I even removed it to clean it. I scraped it off because there were deposits on it. I even cleaned out the cabinet, still nothing. Is it a possibility that the burners are not getting the signal from the thermostat? How would I go about testing this? I have a Radio Shack 22-221 multimeter just let me know the settings and I could check that out. Thank You
Turn the thermostat on and take a volt reading across the gas valve. If the circuit is closed you should have 24 volts. If no volts put a jumper across the thermostat wires and take a read again. If still no read install a jumper at the ends of the two wires from the pilot. One may go to the gas valve and the other may be connected to one of the thermostat wires.
Does the pilot look like it is clean and i
mpinging on the bi-metal strip in the pilot. This type of valve does not make an audible sound when it opens and it also takes a few seconds after the circuit is closed.
 
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Old 12-22-08, 04:34 PM
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I'm sorry I am going to need what you told me "dumbed" way down. By thermostat, do you mean the one downstairs on the wall? And when you say "take a volt reading across the gas valve", are you referring to the wire connections on the top of the unit which has the pilot knob? When it comes to heating I am a complete idiot.
 
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Old 12-22-08, 06:43 PM
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There appears to be a bi-metal switch on that pilot assembly.
This switch is what energizes the gas valve. That pilot flame looks very weak and yellow. The heat from this pilot flame is what actuates the pilot switch. That pilot needs to be removed and the orfice needs to be cleaned. That flame needs to be strong and blue.
 
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Old 12-23-08, 05:12 PM
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Originally Posted by starsky1138 View Post
I'm sorry I am going to need what you told me "dumbed" way down. By thermostat, do you mean the one downstairs on the wall? And when you say "take a volt reading across the gas valve", are you referring to the wire connections on the top of the unit which has the pilot knob? When it comes to heating I am a complete idiot.
Thermostat...on wall
Gas valve....2 wires on valve
Did you actually disassemble the pilot, remove orifice and clean inside pilot?
 
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