How To Troubleshoot a Gas Furnace
Most Gas furnaces present fewer operational difficulties that oil burners do. Usually the problem with a gas furnace involves the pilot light, thermocouple, or a part of the electrical system. Gas furnaces have a safety to prevent gas leaks, but it isn’t 100% effective. Sometimes they fail and leak gas into the home.
IF YOU SMELL GAS, GET OUT OF THE HOUSE IMMEDIATELY, LEAVE THE DOOR OPEN, AND CALL THE GAS COMPANY OR FIRE DEPARTMENT TO REPORT A LEAK. DO NOT ATTEMPT TO FIX THE ISSUE YOURSELF. DO NOT TURN ANYTHING OFF OR ON.
To inspect the pilot light remove the panel covering the pilot and gas burners. On some units the pilot light will be coverd by a plug-type door that must be removed to continue. The pilot light controls, reset button, valves and thermocouple are usually located in a cluster on the front of the furnace. The limit switch should be located on the main chamber of the upper furnace chamber.
The Pilot Light
A draft may have put out the pilot light on your furnace. Instructions for lighting the pilot light should be found on the furnace. If you cannot locate the instructions follow this general guide.
- Locate the pilot light assembly.
- Turn the valve off and wait three minutes.
- switch the valve to the ‘pilot’ setting. Hold a match or lighter to the pilot opening while you hold down the reset button. Keep the button pressed until the pilot light buns brightly, then set the valve to ‘on’.
- If the pilot won’t stay lit you may need to clean it. Turn off the valve and inset a fine piece of wire into the pilot opening. Remove the wire and repeat steps 1-3. If the pilot light won’t stay lit, you may have a faulty thermocouple, or may need professional service.
Many types of gas furnace have no pilot light, instead they have an electronic ignition. If this ignition fails, you should call a service professional.
The Thermocouple
The thermocouple is a component next to the pilot light. If the pilot light ever goes out, the thermocouple is there to stop the flow of gas. If your pilot light won’t stay lit first try tightening the thermocouple slightly. Try to light the pilot light. If it won’t stay lit, try loosening it.
If this also fails it probably needs to be replaced.
- unscrew the copper lead and connection nut inside the connection to the gas line.
- Place the new thermo couple into the bracket. Make sure that the copper lead is pointing down. Push the connection nut to the copper lead and ensure that both are clean and dry.
- Tighten both the bracket nut and connection nut, so that they are just a bit tighter than if done by hand.
Limit Switch
The limit switch is a safety on the furnace just below the main chamber of the furnace. If the main chamber gets too hot, the limit switch kicks in, shutting off the furnace. It also shuts the blower off once the temperature drops to a certain point. If the blower never shuts off than it has been switched to the “on” setting, or needs adjustment. If the blower control has been set to “on” switch it to auto. If it is on auto, it needs some adjusting.
To adjust the switch, remove the cover for the control. One side will have a toother dial marked “LIMIT”, leave this one alone. The one marked FAN is what we’re after. You should see two two pointers, the upper should be set at about 115degrees F, while the lower should be at about 90 degrees F.
If you suspect that you have a minor gas leak around your furnace, mix some detergent and water to make a soapy mixture. Then apply this mixture to the gas line and see if any bubbles form. If bubbles form try tightening the line (but don’t over tighten). If you cannot resolve the issue, call a service professional.