When 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…..as 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!
Anyway, on 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!