Green Tractor Talk banner

1 - 20 of 25 Posts

·
Registered
Joined
·
946 Posts
Discussion Starter #1
Well this ain't a computer but might be an electronic switch problem - any heating folks out there on a chilly Saturday morning? My furnace, which is an electric start is giving me fits. Its 12 yrs old now. When I turn the thermostat on it fires the pilot up just fine, but when it heats up the whatever and go to kick on full heat - it goes out. Any advice which part might be old and tired?
 

·
Registered
Joined
·
3,237 Posts
Well this ain't a computer but might be an electronic switch problem - any heating folks out there on a chilly Saturday morning? My furnace, which is an electric start is giving me fits. Its 12 yrs old now. When I turn the thermostat on it fires the pilot up just fine, but when it heats up the whatever and go to kick on full heat - it goes out. Any advice which part might be old and tired?
does the combustion fan start? Are there any error codes?
 

·
Registered
Joined
·
946 Posts
Discussion Starter #3
No the combustion fire (I assume that's not what's working) is when the fire goes out. I don't think min e show error codes, I don't see a digital readout anyway.
 

·
Super Moderator
Joined
·
4,904 Posts
OK, I'm gonna ask for some clarification here. To begin with, I'm guessing this is a NG or Propane forced hot air furnace?

You say you have electric start but then mention a pilot. You don't have both, it's one or the other. Does your furnace have a standing pilot light or is it an electronic ignition?

When you say "but when it heats up the whatever and go to kick on full heat" are you talking about when the blower motor switches on?

Also, maybe this is important/maybe not but since you are OK, is this system also used for air conditioning?
 

·
Registered
Joined
·
3,237 Posts
No the combustion fire (I assume that's not what's working) is when the fire goes out. I don't think min e show error codes, I don't see a digital readout anyway.
check out the combustion fan(or whatever the kids are calling it these days), and make sure there is not a bird or something jammed in it. Make sure it spins free. make sure the combustion air intake is clear.
 

·
Super Moderator
Joined
·
4,904 Posts
P.S. Got a make/model on this furnace?
 

·
Registered
Joined
·
946 Posts
Discussion Starter #7
It is NG. When I turn the thermostat on the fire lights and blows pretty good; but then when it goes to kick the "heat" on I hear a click and it goes out. Sorry, I am not using the correct terms. I will see if the motor works and if it don't, I can pull it out to see if a stupid bird is stuck down in there. I have had birds go down the flue on the gas dryer flue
 

·
Registered
Joined
·
946 Posts
Discussion Starter #8
The flue motor is working fine and is quiet. Its like it is heating up a sensor before it kicks into full heat, that is when it goes out and then goes through the cycle process again.
 

·
Super Moderator
Joined
·
4,904 Posts
OK, just as an FYI, I'm copying this from another site to help you understand what is SUPPOSED to happen:

The heating cycle starts when the thermostat senses that the room temperature is below the setpoint. On newer units, this causes an inducer fan to pull air through the unit establishing adequate combustion airflow. After proper airflow is verified, the gas valve is opened allowing gas to flow. The gas flows through the burners where it is ignited by a spark or the heat from the ignitor. (Older units have what is called a standing pilot which is a small flame that burns constantly to light the gas.)

After the unit senses the flame is lit, the spark or ignitor is turned off. Normally, the gas will burn for approximately two minutes before the blower is started. This prevents blowing cold air out the vents at the start.

After the preset time or at a set temperature, the blower motor is energized and air is blown over the heat exchanger. The air is heated and supplied to the duct system.

When the thermostat senses that no more heat is required, the gas valve is deenergized and the gas is shut off. The blower motor usually runs for another few minutes to cool off the heat exchanger. This can be controlled by either a timer or a temperature switch.

From your description, it sounds like your thermostat is doing what it is supposed to do and your ignition system is working fine.

So it sounds like you have an air flow problem. If it is a combustion air flow problem the burner shouldn't light to begin with but it's possible that your air flow there is borderline. There is also an air vane somewhere in your room air blower system. If your filters are clogged or all of your room vents are closed (for example) you won't get enough air flow circulating and that air vane will shut down the system.
 

·
Administrator
Joined
·
17,325 Posts
Often there is a LED on the board to flash codes. What make/model is it? RGD is our resident HVAC expert.
 

·
GTT's Pilot in Command (PIC)
Joined
·
8,558 Posts
All that I know about the electronic pilot light ones is that, if the heating portion does not ignite within so many seconds of the pilot light being on and triggering the ignite for the main burner, it is designed to shut down, to prevent possible gas build up and "explosion". Might check that the main burner is free of rust and debris, if possible.
 

·
Registered
Joined
·
2,160 Posts
There is a flame sensor rod ....not the thermocouple....that hangs in the flame . This is probably dirty. Take it off and sqower it with a brillo pad....or sand paper. This sensor takes over when the main flame kicks in. If it cant sense flame,cuz its dirty or bad, it will drop the gas valve off. The sensor rod builds up microvolts when heated as its dissimiliar metals....if the outer metal is dirty,it cant do its job and tell the gas valve.....hey I've got flame....keep on keeplng on. And will not hold the coil in


This sensor I'm referring to has a time delay on it. It usually about 20-30 seconds. This gives it time to heat up and make voltage. So it definitely sounds like this could be your problem...

Look for a wire going near the gas tubes/flames...the sensor itself is usually silver about the size of a pencil lead thickness and bent into an ell shape. It will have a spade/flag terminal on the end. Usually its below the burners away from the pilot some
 

·
Registered
Joined
·
946 Posts
Discussion Starter #13
Its a Trane XB80. I have the cover off where the fire is and see no digital readouts. The fan blower works if I just turn it to "on" in the thermostat, the flue motor kicks on fine, the pilot lights fine, but after about 40 seconds, the fire goes out. Sounds like at the same time it is kicking into a next level of heat
 

·
Registered
Joined
·
946 Posts
Discussion Starter #15
Ya, its like the main burner is not kicking in. So does that heat sensor, on the outside, look like a ceramic rod about the size of a thin pen, with one wire going to it? That's my gut at this point....
 

·
Registered
Joined
·
2,160 Posts
If that doesnt fix your problem, there could be a manually reset microswitch open. There are 2-3+ of these scattered around near the flame. They are all in series and if one of them get too hot it will open up and kill the circuit. They are about the size of a quarter and will have a dark red tiny little switch on it. push in on the switch...if you hear a click, then it was open. These protect the system if things get too hot in the control cabinet...or the flame rolls out of the exchanger. One is usually on the flue pipe to protect if the flue becomes clogged amd gets too hot, one is usually at either end of the burner header, sometimes one is above the burners, for flame roll out...etc
 

·
Registered
Joined
·
946 Posts
Discussion Starter #19
Ok, I pulled it out, it is quite long and has a 90 degree turn. I expected it to be crusted up but it "looks" clean - does that mean anything? Or could it just be bad?
 
1 - 20 of 25 Posts
Top