When a furnace goes unused for a few years, it takes a little extra work to make sure it's in proper running order. Because problems with an old and malfunctioning furnace can range from inconvenient to dangerous, it's best to take these steps of furnace maintenance before it's time to start running your furnace regularly.
Check and Replace Air Filter
An old air filter is one of the first things that should be checked and replaced as necessary. If it's been sitting for a few years, it should be replaced even if the furnace itself wasn't in use. Dirty filters quickly start to lose their effectiveness, and they can also create additional strain on your furnace by reducing airflow into the furnace. If instead there is no filter at all, one should be added before you run your furnace, as it's important to keep as much dirt and dust out of your furnace as possible.
Check Carbon Monoxide Detector
A functioning carbon monoxide detector is a vital part of every heating system. Some byproducts of the heating process are toxic gasses that are ordinarily vented safely outside your home, but in the event that this does not happen, it's important to make sure you have a way of being alerted to the presence of these gasses. Carbon monoxide has no color and no odor, which makes it particularly dangerous. If you don't have one installed or suspect the one you have no longer functions, contact an HVAC specialist to inspect it.
Clear Condensate Drain System
Furnaces, like air conditioners, drain moisture as they operate, and this moisture needs to be able to safely flow out of your home. Blocked condensate pipes or drains can cause this moisture to back up, which has the potential to damage both your furnace and house.
If you have easy access to your furnace, you can sometimes test if your drain pipes are in good shape by pouring water down them. If none backs up, they should be good to go. If you're dealing with a stubborn clog or if you can't access your drain pipes and hoses, a technician can inspect and clean them out for you.
Check Thermocouple and Flame Sensor
The thermocouple and flame sensor together are responsible for making sure the furnace's pilot light stays lit and that the supply of gas flows smoothly. If these parts malfunction, the pilot light might repeatedly go out or your furnace may shut off early due to the gas being repeatedly cut off. These parts are generally easy for a technician to clean or replace, but can still cause your whole furnace to stop working until they are fixed. It's a good idea to have these parts inspected and fixed before running any furnace that has been shut off for long periods of time.