How to troubleshoot a gas furnace | Trane XR80

How to troubleshoot a gas furnace

Trane x80 gas furnaceWhen you wake up on a cold winter’s morning to find your vents blowing nothing but cold air, everything else on the day’s “to-do list” takes second place to fixing your heater! This recently happened to us, and instead of working (I work from home), I decided to fix it myself. So in this article, you’ll learn how to troubleshoot a gas furnace.

Now before I get into the basics of troubleshooting a gas heater, I’d like to address the warning mechanism Trane has in place to notify the homeowner of an error. Instead of a nice little beep or an orange or yellow light coming on, Trane has decided to blow cold air to let you know that something’s not right. Here’s my thought process on that… if it’s not bad enough that the heater went out, now they have to blow cold air to cool your house down even more. Let’s freeze them out of house and home…that will get their attention!

Just dumb.

Anyway, one with my “how to.”

How to troubleshoot a gas furnace

My particular furnace model is a Trane XR80. Note: I am not a professional. So take that into consideration before you attempt any of these troubleshooting steps. If you still have the manual which came with your furnace, refer to their troubleshooting section for additional help.

The first thing I ALWAYS do when something stops working is take it apart. So, I removed the two front panels of my furnace to see what was working and what was not. The infuser started up and the surface ignitor started glowing, just as it always should, but for some reason, the gas valve was not letting gas in. So I turned my kitchen stove on, also gas, to make sure the gas was on and made sure the gas valve on the inlet hose was open. So right away, I knew it had to be something to do with the gas valve.

Every Trane furnace has a blinking light on the control panel. It can actually be seen through a little looking glass hole in the bottom panel. Whenever there’s an error, the light will have a unique blinking sequence. That code can be used to troubleshoot the problem. BUT, there’s a secret to viewing the code. If the furnace doesn’t start the first time, it will attempt two more times. That means the infuser (fan sound) will turn on and off three times. After the third time, the error code will flash. It’s usually two flashes, then a pause, or three flashes, then a pause, etc.

Here’s a break down of what those flashes mean:

Flashing Slow Normal – No call for Heat from thermostat
Flashing Fast Normal – Call for Heat from thermostat
Continuous ON Control Board Bad – needs replaced
Continuous OFF Check Power
2 Flashes System Lockout (Retries or Recycles exceeded)
3 Flashes Vent Pressure Switch Error
4 Flashes Open High Temperature Limit Device
5 Flashes Flame sensed when no flame should be present
6 Flashes 115 Volt AC power reversed or Poor Grounding
7 Flashes Gas valve circuit error
8 Flashes Low flame sense signal
9 Flashes Check ignitor circuit and line “N” to 24 VAC Common voltage ( < 2 volts)
(possible grounding problem)

Once you know the error code, call the service number on your furnace for advice on repairing it yourself. A service call from a heating/cooling company can cost you $100 or more, not including parts, if any are needed. If that’s in your budget, that might be your best option, because you might replace unnecessary parts on your own, or, make things worse!

I actually called the service number and went through the troubleshooting process with a technician on the phone. We narrowed it down to having a faulty gas valve. The code I was receiving from the heater was two flashes, which basically means that everything else, besides the valve, was ruled out.

I hope this information has been helpful!

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David Allred has been working from home as an internet marketer, blogger and serial entrepreneur for nearly a decade. In addition to writing occasionally on GoodIdeasandTips, he spends most of his time with his family, volunteer coaching, hooping it up or eating cookies.

12 Responses to “How to troubleshoot a gas furnace”

  1. Hershel Soden says:

    So why did you leave the rest and best of the story out,did you replace the faulty value.

  2. David Allred says:

    Sorry Hershel! The valve went out right as the weather started warming up here in Arizona. So I haven’t replaced it as of yet. It’s $100 bucks I can use for something else until November/December.

  3. sheila says:

    Hi. My trane furnace was blinking green 3 times with water in the bottom. Repair guy replaced the 650.00 motor twice and still no heat? I didn’t pay him yet wondering if the motor wasn’t the problem?

  4. David Allred says:

    Sheila, I’m no expert, however, I don’t think the motor is the problem if you are seeing water in the bottom of your furnace. Whoever installed it should have added a drain pipe of some kind.

  5. Walter Cibulski says:

    I have a Trane XR90 code flash 3 times Replaced pressure switch, Replaced Inducer motor, Replaced sail switch on inducer motor, replaced hoses still flashes code 3?

  6. Melissa Doutt says:

    I have the same furnace AND the same error code…did you replace the valve? Any tips?!?! We are getting up to 55 today in Ohio…but by Tuesday we will drop to 27…I need a new valve ASAP!!

  7. David Allred says:

    My advice is to start with the basics first and then work your way up. First step is to make sure your furnace is getting gas. In most cases, that’s the main issue. Check the circuit board for any burnt or melted components. If you’re getting gas and the circuit board seems fine, you can remove the valve and have it tested at your local HVAC company. Some will test it and others won’t…so call ahead of time.

    If all else fails, and you’re not confident in removing the valve yourself, call an HVAC tech to come out and take a look at your system.

    Good luck!

  8. julie says:

    I have experienced the same issue with the 3 flash error alot recently. It’s usually a bad connection on the control board where the 9 wire plug goes in. Wiggle plug around and it may fore up but you will need to have board replaced as it will happen again.

  9. Caryn says:

    Love the way Trane blows cold air to make sure we get plenty cold before we realize the junk thing isn’t working properly. Way to go Trane…morons!!!!

  10. paul stocks says:

    Hello David

    The issue I have is the furnace does blow warm air when thermostat is on heat and set to a heat temperature as the same works other way round with cool. It cools also as normal per the thermostat. The problem is the furnace continuously blows air even when thermostat is turned off. The red led continuously blinks, but unsure if it’s a fast or slow blink.

    Hope you can help.

  11. warren says:

    Hello David,My heater has 6 blinks,it was working fine before.I never touched it but 6 blinks means the polarity is reversed…a friend said I need to replace the control board,is that true,Please help,Thanks….

  12. David Allred says:

    Hi Warren, I wish I was of more help. Most of the time, if you call a local dealer for Trane, and tell them what it’s doing over the phone, they’ll give you their best guess without charging you for it. That’s what I would do in your instance.

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