Few things in life are as frustrating and as uncomfortable as waking up cold in the dead of night because your furnace has suddenly started acting up or turned off by itself for no apparent reason.

The good news is, you can troubleshoot many furnace problems even if you don’t have a background as an HVAC technician. Read on to learn what to look for when troubleshooting a problematic furnace, but keep in mind that this is just an informative article, not a repair guide. If you’re thinking of having a furnace repaired or replaced for a system with a cutting-edge features, consult HVAC experts.

Here’s a simplified guide how to troubleshoot a furnace:

Step #1: Check the filters

Every HVAC system contains one or more air filters that are designed to prevent dust, dirt, debris, pathogens, fungal spores, and other filth from getting into our homes. However, if these filters aren’t replaced regularly (or cleaned, if they’re reusable), they will inevitably become clogged.

Dirty air filters will impede airflow, make your furnace less energy-efficient, make it more likely to break down or refuse to turn on, and may even become a fire hazard. Regularly checking your filters and replacing or cleaning them as-needed is crucial in order to keep your HVAC system working properly.

Step #2: Take a look at the thermostat

It goes without saying that your thermostat should be using the “heat” mode during winter. If the “heat” is turned on, check the thermostat’s batteries and replace them if necessary. Make sure your thermostat isn’t getting any false readings from lamps, sunlight, space heaters, ovens, or other heat sources.

Step #3: Is the furnace getting power?

Go to the furnace switch (it should be located close to the furnace itself) and make sure it hasn’t been turned to off. If that doesn’t help, check if the power is turned on at the fuse box or the breaker box.

When everything is at should be, all the breaker switches on a breaker box should be pointed in the same direction. If you have a fuse box, and some of the fuses are discolored or melted, that’s a sure sign that some parts of your home aren’t getting electricity.

A word of warning: before you try to reset power, make sure your hands and feet are 100% dry. If you notice signs of moisture or electrical damage, or you simply don’t feel comfortable doing this yourself, call in a registered electrician ASAP.

Step #4: What’s the color of the furnace flame?

The flame in your furnace should be blue and maybe have a small yellowish tip. If the flame is yellow, green, purple, red, or any other color that’s not blue, get in touch with a qualified HVAC professional immediately. NEVER attempt to fix the color of your furnace flame on your own.

Step #5: Make sure there aren’t any leaks

If the flame in your furnace is out, turn off the gas and leave it like that for a quarter of an hour or so. If you can still smell the gas, there’s a chance that your furnace may be leaking, in which case you and your loved ones should get out of the house as quickly as possible.

Once you’re outside and at a safe distance, you should alert the fire department and your gas company, and have them deal with the problem.

Step #6: Are any of the heating ducts obstructed?

Heating ducts should never be covered or otherwise obstructed by rugs, furniture, clutter, or anything else that can block airflow. In addition to preventing warm air from being properly distributed throughout your home, obstructed air vents can cause your HVAC system to break down prematurely.