Heating systems are usually trouble-free and easy to maintain. But efficient operation is a function of good regular maintenance. No matter what type of furnace you have, there are several things you can do to keep your heating system in top condition.
While some aspects of furnace upkeep can be complex and are best left to the professionals, there is a surprising amount of repairs you can do yourself. Keeping your furnace running properly can save you a lot of money on heating costs and helps avoid expensive repairs in the future.

Before we get to the troubleshooting, let’s start with some steps you can take before your furnace shuts down.

Cleaning a Furnace

Dirt is the biggest enemy of your furnace. It can waste fuel and drastically lower efficiency. In some cases, it can even cause the furnace to overheat.Dirt affects all three basic components of your furnace, so cleaning is the most important part of regular maintenance. The three parts of the furnace that should be cleaned: the filter system, the blower and the motor.
The furnace filter should be replaced or cleaned at the beginning of the heating season and about once a month during periods of continuous use .To check the filter, take it out and hold it up to the light. If it looks clogged, replace it with a new filter of the same type and size regardless of the length of time it has been used.

A disposable furnace filter consists of a fiber mesh in a cardboard frame. The size of the filter is printed on the edge of the frame. An arrow on the edge of the frame indicates the correct direction of airflow through the filter. Air flows from the return-air duct toward the blower, so the arrow on the filter should point away from the return-air duct and toward the blower.

A permanent filter is usually sprayed with a special filter-coating chemical, available at hardware stores and home centers. Clean this type of filter according to the manufacturer’s instructions, which are usually attached to the furnace housing. Here’s how to replace a filter:

• Look for a metal panel on the front of your furnace below the return-air duct, between duct and blower system. The panel may be marked “filter,” or it may form a lid or front of a boxlike projection on your furnace housing.
•  Slip the panel off its holding hooks, or unscrew the panel from the box or furnace housing. On some heating units, filters are exposed; in that case, just slip the filter up and out of the U-shape tracks that hold it in place.
• Inspect and replace or clean the filter, depending on type.
• Clean the blower assembly, belts and pulleys to the blower and motor housing. Cleaning the blower is critical if your furnace has a squirrel-cage fan, because openings in this type of blower often become clogged with dirt. To clean your blower, remove the panel that covers the filter to gain access to the blower or panel on the front of your furnace. This panel may be slip-fit on hooks or held in place by a series of retaining screws. Access to the inside of your furnace blower is usually gained by sliding out the fan unit, which is held on a track by screws.

How to Troubleshoot a Gas Furnace

Natural gas and propane burn cleaner than fuel oil, and most gas furnaces present fewer operational difficulties than oil burners do. In fact, the problems that affect gas furnaces typically involve the furnace’s thermocouple, the pilot light, or some component of the electrical system.

Gas furnaces and heaters have control shutoffs to prevent gas leaks, but they are not fail-safe. If you smell gas in your house, do not turn any lights on or off and do not try to shut off the gas leading to the furnace. Get out of the house, leaving the door open and immediately call the gas company or the fire department to report a leak. Do not re-enter your home.

On some gas furnaces and heaters, a plug-type door covers the pilot light assembly. To gain access to the pilot burner, pull the door out of the furnace housing. On other units, remove the panel that covers the pilot and gas burners.

The pilot light controls, reset buttons, gas valves and thermocouple are usually contained in an assembly at the front of the furnace. The furnace limit switch is located on the plenum (main chamber) or main duct junction on the upper housing of the furnace. The pilot light on a gas furnace can go out because of drafts. To relight the pilot, follow the manufacturer’s instructions exactly; they’re usually fastened to the furnace. If instructions for relighting the pilot are not provided, follow this general procedure:

• Find pilot light assembly. It typically has a gas valve with ON, OFF and PILOT settings.
•  Turn the valve to the OFF position and wait three minutes.
•  Switch valve to PILOT setting. Hold a lighted match to the pilot opening while you push the reset button on the pilot control panel. Keep this button depressed until the pilot flame burns brightly, then set the valve to the ON position.
•  If the pilot flame won’t stay lit, the opening may be clogged. Turn the gas valve OFF and clean the opening with piece of fine wire. If it won’t stay lit after several attempts, you may have a faulty thermocouple. If the pilot flame still won’t stay lit, call a professional service person.
  Some furnaces have an electrical system to ignite the gas; in these systems there is no pilot light. Instead, an electric element heats up and ignites the burners. If this electric ignition system malfunctions, call a professional service person.