When your gas furnace suddenly stops heating, the first thing you should do is check your pilot light. If it has blown out, re-lighting it often solves the problem immediately. If it does not re-light, then you know you have to call someone to fix either the pilot light itself or the associated gas valve. What do you do, however, when the pilot light is lit, but the furnace is still not blowing out hot air? Blame your thermocouple, of course.
What is a thermocouple?
The thermocouple is essentially a safety sensor. If the pilot light is not burning, it prevents the gas valve from opening and giving the burner fuel to burn. This is to prevent gas from leaking out and causing problems. When the pilot light is lit, the thermocouple should let the gas flow to the burner. However, when it malfunctions, it may inhibit the flow of gas even when the pilot light is lit. Without a gas supply, your furnace has nothing to burn and won't heat your home.
What kinds of problems cause the thermocouple to malfunction like this?
The thermocouple just looks like a v-shaped piece of wire. It's not a very sturdy part, and it is not unusual for it to malfunction, even when a furnace is relatively new. The thermocouple may break, become bent, or become un-reactive because it is coated in soot or debris. One thing is for sure -- if it is not properly sensing that your pilot light is lit, it won't let your furnace kick on.
What should you do if you think you have a problem with your thermocouple?
You can start by trying a few quick fixes yourself. Turn the pilot light off and give the furnace some time to cool down. Then, wipe the thermocouple off with a cloth to remove any soot or debris. (Look in your owner's manual to locate the thermocouple. It is near the pilot light and, as mentioned above, is v-shaped). Then, turn the pilot back on and see if the main burner lights.
If cleaning the thermocouple does not work, turn the pilot back off again. Let the furnace cool, and then use a wrench to make a slight adjustment to the bolt at the base of the thermocouple. If the thermocouple was jostled out of alignment, this might fix the issue. Switch the pilot back on. If the furnace ignites, you're all set. If not, it's time to call your HVAC contractor, as you likely need a new thermocouple.
For more information, contact River City Heating & Cooling or a similar location.