More Heating, Air Conditioning, Fridge, HVAC Answers
Question Library
Ask a question about Heating, Air Conditioning, Fridge, HVAC
Volunteer
Experts of the Month
Expert Login
Awards
About Us
Tell friends
Link to Us
Disclaimer
|
| |
|
|
| |
| | | |
About Jim Barnhart
Expertise
Fifty + years in Heating, Ventilating, Air Conditioning, Sheet Metal Manufacturing.
Semi retired since 1995,
Experience
Answer questions about , residential and commercial.
Answer questions about sheet metal fabrication.
Fifty years plus experience.
No answers for oil equipment, No answers for kitchen appliances, No answers for laundry appliances.
Education/Credentials
Hands on since 1950
| | |
| |
You are here: Experts > Home/Garden > Home Appliances > Heating, Air Conditioning, Fridge, HVAC > heater
Expert: Jim Barnhart - 11/2/2009
Question
QUESTION: Hello Jim Barnhart,
I have a Trane XR80, natural gas,forced air furnace, about 7 years old. Right now it has an intermittent problem which I'm sure will only get worse.
When it starts up, the vent fan motor starts, the glow plug comes on (which is all normal), but the burner fails to light - the gas valve isn't opening. Then the blower fan starts blowing right a way and the glow plug goes out. The sequence just skips the lighting of the burner. When it fails to light and just the blower is on, I have to reset the furnace - turn off the power for a few minutes. Sometimes it fixes the problem, sometimes I have to reset again, and some times it will run through a few more cycles after a reset,then I have to reset again.
I know there are two wires coming from the top of the gas valve. It's not really a coil, I'm not sure what it is. Gas valve, pressure switch? WHAT DO YOU THINK???
Thank You,
Rick
ANSWER: Rick,
Everything you say that is happening is the normal way it should for a furnace that the burner doesn't light
I'm thinking that the igniter may not be positioned close enough to the burner for the burner to light in time before the flame sensor shuts the gas off.
Check the igniters position, check for covers being off causing a draft, check for any obstruction in the burner opening.
If the pressure switch wasn't working the igniter wouldn't glow.
I doubt if it's the gas valve but it's possable, you should be able to hear if any gas flows for a split second if you listen closely.
---------- FOLLOW-UP ----------
QUESTION: Jim Barnhart,
The ignitor looks to be fine. Nothing looks out of place. On this furnace, there is a flashing red light, to help diagnose a problem. When it will not light, it flashes 4 times, which according to some of my furnace papers that I just found, say 4 flashes is an "Open Temperature Limit Switch"
What and where is the Temperature Limit Switch?
Thank You
Rick
Answer
Rick,
A "Temperature Limit Switch", there are several "Temperature Limit Switches" that open when the furnace over heats or doesn't heat when it should, how many and location for your furnace I don't know?
Going back to my original answer the problem is that your burner doesn't light not even for a second which would rule out a "Temperature Limit Switch" that opens from over heating, that only leaves the "Temperature Limit Switch" that closes from heat like a thermocouple on the older pilot lights, the way it works is that the igniter lights the burner, the burner heats the flame sensor, the flame sensor activates the "Temperature Limit Switch" which allows the burner to stay on.
There is only a split second that the gas valve will stay open if the burner doesn't light from the igniter the reason being that you don't want a build up of raw gas.
Either the gas valve is faulty, or the igniter isn't hot enough, or the gas can't reach the igniter fast enough.
Ask a Question
|
|
