Coleman produces gas furnaces in a variety of models and sizes, all designed for high-efficiency home heating. Each model includes a pilot light assembly with a thermocouple – a heat sensor that connects to both the pilot light and the incoming gas supply line. If the thermocouple doesn't sense heat coming from the pilot light, it shuts off the gas to prevent a leak or dangerous buildup. If your home furnace's pilot light won't stay lit, it's possible that your thermocouple has failed and should be replaced. Luckily, this is a relatively simple procedure with the right tools and equipment.
Before attempting to replace your furnace's thermocouple, check the owner's manual that came with your furnace. It will provide you with the exact model of your furnace and may contain a list of compatible parts in the back as well as warranty information. If your furnace is still under warranty, it's advisable to call a Coleman service technician to complete the repair, particularly if you have little experience in home appliance repair. If, however, you need to perform the repair yourself, use the compatible part number and furnace model number to order a replacement thermocouple. This will either be a Coleman-produced part ordered directly through the manufacturer's website or a model-compatible "universal" thermocouple purchased from a home repair or heating supply shop or similar website.
Once you've acquired the replacement thermocouple, begin the repair process by tracing the gas line from your furnace until you find a shutoff valve. Turn the handle or knob completely clockwise to shut off the gas entirely, and then use your breaker box to shut off power to the furnace. Give the furnace an hour or more to cool down. Even if your thermocouple has been malfunctioning, it may still be incredibly hot at the time of power shutoff.
Locate the pilot light access panel near the bottom half of your furnace and remove it by lifting it up and pulling it off. Certain models may require you to unscrew the panel from the furnace before lifting it. Look inside to locate the thermocouple that's connected to the pilot light – it resembles a piece of straight metal tubing that's smaller than an average-sized soda straw. Disconnect the thermocouple by removing any copper leads attached to it and use an adjustable wrench to remove the nut that's securing the thermocouple to the pilot light's bracket. Pull it off the bracket and unscrew the nut that's connecting the other end of the thermocouple to the furnace's gas supply line. Remove the thermocouple and dispose of it.
Replacement and Reset
Once you've removed the old thermocouple, check the connections and parts that were attached to it. If they're dirty, clean them before installing the replacement thermocouple. Attach the thermocouple's larger fitting to the incoming gas line and secure it tightly with a nut, then connect the other end to the pilot light's bracket. Secure it with a nut and, once you've ensured all connections are tight, open the gas shutoff valve, restore power to the furnace and relight the pilot light – if the thermocouple is half an inch inside the pilot flame and the furnace is starting to operate, your installation is complete. Turn the furnace off, replace the access panel and enjoy your repaired furnace.