Furnace Repair

Safety first: gas smells and carbon monoxide alarms

If you smell gas, leave the house now. Do not switch lights or appliances on or off. Once you are outside, call 911 and your gas utility. If a carbon monoxide alarm sounds, or people in the house have headaches, dizziness or nausea that ease when they go outside, get everyone into fresh air and call 911. Do not go back in until responders say it is safe. Then call us to find the cause. The furnace can wait. Your safety cannot.

No heat: the usual causes

Many no-heat calls come down to a handful of causes. A clogged filter can make the furnace overheat and shut itself off. A dirty flame sensor lets the burners light and then cuts them out after a few seconds. Hot surface igniters crack with age. Pressure switches, inducer motors and blower motors wear out. On a high-efficiency furnace, a blocked or frozen condensate drain stops the system, and during a storm the vent pipes outside can be blocked by snow or frost. Many furnaces flash a code through a small window on the cabinet. Tell us the pattern when you call and it helps us bring the right part.

Before you call

• Check that the thermostat is set to heat and the set point is above the room temperature.
• Replace the filter if it is dirty.
• Make sure the furnace power switch, which often looks like a light switch on or near the unit, is on.
• If your furnace vents through a side wall, clear snow and ice from the pipes outside.
• Do not remove panels or try to light the burners by hand on a modern furnace.

Cracked heat exchangers

The heat exchanger is the metal chamber that keeps combustion gases separate from the air that moves through your house. After years of heating up and cooling down, it can crack. A crack can let carbon monoxide into the air stream, which is why we inspect the heat exchanger on any furnace that is old, overheating or showing signs such as soot or a flame that wavers when the blower starts. If we find a crack, we show it to you with a camera or photos, and we shut the furnace off, because running it is unsafe. Many manufacturers cover heat exchangers under a long warranty, so we check that before we talk about replacement.

Altitude and your furnace

Gas burns differently in thin air. Furnaces at the elevations around Denver have to be set up for altitude, usually with the gas orifices or settings listed in the manufacturer's high-altitude instructions. A furnace that was not set up correctly can run hot, produce soot or carbon monoxide, or wear out its heat exchanger early. We check the gas pressure and the burners as part of every repair, not just the part that failed.