thermocouple or flame sensor??? PLEASE HELP

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thermocouple or flame sensor??? PLEASE HELP

Postby livengood » Fri Nov 11, 2011 11:12 am

Hello.. I'm tring to figure out if i have a thermocouple or flame sensor in my furnace. Its prob 15-20 yrs old. upon lookin@ the furnace it looks to be a standing pilot assembly, it has a pilot burner and what looks to be a thermocouple but it has ceramic on it like a flame sensor and is connected by a thick orange wire with a screw on attachment at both ends not a copper tube. The tip is also very short 1/2 inch or so....Been doing research because My furnace fires up then 5 seconds later it clicks off then few seconds later fires up again and does this over and over until the cycle ends. It does not do it all the time sometimes its one or two clicks and others its for the entire cycle duration... I did clean the tip off with steel wool and was hoping this is the problem but dont know what replacement to look for cause everything i have seen for a thermocouple is a copper tube attached to it and the flame sensors have a flat metal prong with a hole at the end... please help me...
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- thermocouple or flame sensor??? PLEASE HELP

Postby Freon » Fri Nov 11, 2011 12:34 pm

Have someone call for heat at the thermostat while you look and listen as the furnace tries to light. I think you may have a spark ignition so the first thing I think you will hear is the tick, tick of the spark (you may be able to see it) and one metal click as the pilot part of the gas valve opens. Then you should see the pilot light ignite. Then you may hear the click of the gas valve again and the pilot will be extinguished.

Tell us if what I describe is accurate. Then we'll know better how to help. The more you tell us, the better we can assist you. What happens and when as the furnace tries to light is very important. Make and model of the furnace is very helpful too.
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- thermocouple or flame sensor??? PLEASE HELP

Postby livengood » Fri Nov 11, 2011 3:18 pm

ok. Its a Thermo Pride IGH7-100 Yes it is a spark ingition. When it starts up i hear a click n see the spark then it lites the pilot then another click it lites the burners.. I stayed steady the whole time until the blower motor kicked on then all burners n pilot went out started the whole cycle of lighting pilot n the burners again over and over until the blower kicked off... there is a piece of metal the shape of a 3 connected to the housing of the pilot and ignitor whitch sits just beyond both the pilot and ignitor, it does glow red...is that the sensor??? could that be the problem?
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- thermocouple or flame sensor??? PLEASE HELP

Postby Freon » Fri Nov 11, 2011 3:43 pm

I am going to assume you have a flame rectification system for proving flame. Make sure all wires to the pilot/spark unit are well secured. The usual problem with this type of flame proving system is the current flow through the pilot flame may become too weak for the control board and it thinks there is no flame, thus shutting everything down. The coincidence of the blower motor starting and the system shutting down may be due to the accompanying voltage drop with the blower starting and that voltage drop causes a decrease in the flow of current through the pilot.

Here's a test to see if I may be right. Set the blower at the thermostat to ON. Then, while the blower is running, call for heat and see if the furnace behaves like it has been... shutting down after a few minutes of operation.
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- thermocouple or flame sensor??? PLEASE HELP

Postby livengood » Fri Nov 11, 2011 4:21 pm

I still have an oldschool round thermostat... I should prob start by getting a new one....right???
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- thermocouple or flame sensor??? PLEASE HELP

Postby Freon » Fri Nov 11, 2011 4:42 pm

Nothing wrong with old-school... very dependable simple technology. Take a look at the front of your furnace. See if there's a box about 5"x2"x1"deep. That could be your high limit fan control... again old-school but if it's there it may have a small (1/4" diameter) plastic stub protruding from the case on the front. If you pull that, it will start the blower. Some don't have that "pull" but you may be lucky. If you feel comfortable with electronics, there's another way to get the fan to be on but it involves a jumper wire between 2 terminals at the furnace.
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- thermocouple or flame sensor??? PLEASE HELP

Postby livengood » Fri Nov 11, 2011 5:03 pm

i think its there.. is it usually a metal box?
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- thermocouple or flame sensor??? PLEASE HELP

Postby Freon » Fri Nov 11, 2011 5:22 pm

Yes, usually aluminum. Look at the edge along the long sides. If you squeeze the cover in the middle and gently pull toward you, it will come off revealing a dial. However if you don't see the small "pencil" protruding from the cover (only protrusion) then it doesn't have a blower control.
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- thermocouple or flame sensor??? PLEASE HELP

Postby livengood » Fri Nov 11, 2011 6:04 pm

yes ive seen it. n it has a button on it too
. i have 2 kids so havent been able to make it down there yet... dinnertime.. lol
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- thermocouple or flame sensor??? PLEASE HELP

Postby meard421 » Sat Nov 12, 2011 8:04 am

Its prob 15-20 yrs old. upon lookin@ the furnace it looks to be a unfelled flier building, it has a guide burner and what looks to be a thermocouple but it has instrumentality on it similar a shine sensor and is siamese by a gelatinlike chromatic wire with a rotate on affection at both ends not a metal conduit. The tip is also really close 1/2 progress or so....Been doing search because My furnace fires up then 5 seconds ulterior it clicks off then few seconds later fires up again and does this over and over until the bike ends.
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