13 Best Tips on How to Troubleshoot a Furnace


Crucial to combating cold winters, a working furnace keeps your home and everyone in it comfortable and warm no matter what the temperature is outside. Like any other system, occasional tune-ups and maintenance are required to keep it working strong and efficient. Despite one’s best efforts, a furnace break-down can still happen.

Here is a comprehensive guide how to troubleshoot a furnace:

1. Set the Thermostat to ‘Heat’

If you’ve just turned on your furnace for the winter and you find it’s not functioning, look to the thermostat. Sure, it’s obvious but double-check it. Believe it or not, it does happen that homeowners don’t switch from ‘cool’ to ‘heat’ and that’s the problem.

2. Check the Power

Is your furnace getting electricity? Here’s how to check and troubleshoot the furnace. First, look to your thermostat. There is a ‘on’ or ‘auto’ switch. Turn the switch to ‘on’. This should immediately kick on the fan. If it does, electricity’s not your problem. If it doesn’t, it’s an issue with your power somewhere along the way.

3. Check the Fuse Box

Another way to check for power is to verify the fuse box is still supplying electricity to the furnace. Look for the HVAC breaker. Make sure it’s on. If it’s not, switch the breaker back on. If the fuse is melted or discolored, the fuse itself will require a replacement. Ask a furnace repair service to help you with the fuse box replacement.

4. Check the Air Filter

The air filter gets dirty over time. That’s sort of its job. Dirt, dust, and hair from pets can clog a furnace filter. By not switching it out for a new one, you run a risk of fire hazard or even a breakdown due to excessive dirt or dust. Hold your filter up to a light source. If no light is passing through, a replacement is required.

5. Check Furnace Flame

Do not attempt to fix your furnace flame. Always look to professional help. That said, you can examine the color of it. It should appear a healthy blue, with or without yellow at the tip. Blue indicates it’s burning like it should. If it’s red, yellow, purple, or green, shut it down and call a technician.

6. Relighting the Pilot

If the furnace flame is out, you will need to relight it. Be careful. Look at the instruction manual before trying anything like this. Turn off the gas for 15 minutes prior. This will clear away any gas from the area. From there, light the pilot light and see if it works. Homeowners that aren’t comfortable doing this on their own, no worries. A professional can handle this task.

7. Check the Gas Valve

Verify that the gas valve is in the ‘on’ position. There should be a valve somewhere within two meters of the furnace. It’s very unlikely the valve has been touched but all the same, double-check. You may find this to be your fix and then you save yourself from having to pay for a technician’s service call.

8. Look at the Furnace Code

Any furnace built after 1990 has a window that shows a light. This light may flash a code. Note the code. Open a furnace’s access panels. Inside, there should be a guide that indicates what a given code means. This will help identify what’s going on and will be something you can tell a technician when you’re making the appointment.

9. Check the Front Panel

Some furnaces will not turn on if the front panel is open. Ensure it is full pressed in and properly secured.

10. Check Vents and Registers

Blocked vents and registers can lead to duct leaks from above-average air pressure and potentially be a source for early repairs or furnace break-downs. If you have rugs, furniture, or materials covering these areas, remove them. Your furnace may be running but the air’s can’t get around the home. Whether a ductwork repair is needed, blocked vents and registers are a sign.

11. Turn the Furnace Switch Off

Before doing any work in your furnace, be sure to have the thermostat off and shut down the furnace. It’s a major safety hazard if you intend to do any serious troubleshooting while the furnace’s active.

12. Oil the Furnace Blower

A lubricated blower is used to move heat from a furnace and distribute it to various areas. To oil it, turn off the furnace at the circuit breaker. Remove the access panel. Locate the blower. Remove the bolts securing it and pull the motor from its housing. Locate the oil ports and then squeeze a few drops into each port. There should be one on the motor and shaft. Now close everything up and turn the furnace back on. The blower motor will run more efficiently having been lubricated.

13. When to Call A Professional

When to call an HVAC technician will vary person-to-person. Ultimately, when you have to troubleshoot in a way that makes you uncomfortable or feel unsafe, that’s the time to make the call. It doesn’t hurt to have an expert eye looking at your furnace. Needless to say, they will be able to identify and resolve the issue in a much timelier manner as well.


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