When temperatures plunge in Missoula and winter storms roll through, the last thing any homeowner wants is a furnace that suddenly stops working. Unfortunately, cold snaps often expose issues that may have been quietly building for weeks or months. The good news is that there are a few simple checks you can perform before calling for service — and in many cases, you may be able to get the heat back on quickly.
Below are the top troubleshooting steps our technicians recommend when your furnace shuts down during extremely cold weather.
1. Start with the Furnace Filter
One of the most common reasons a furnace stops running — especially during long stretches of cold weather — is a clogged or overdue filter.
Over time, furnace filters trap dust, pet hair, debris, and particles moving through the system. When that filter becomes too dirty, airflow is restricted, and the furnace may shut itself down to prevent overheating.
If your heat goes out during a cold spell, go directly to your furnace and check the filter. If it’s been in place for two or three months, it’s likely time for a replacement. Make sure to write the installation date on the new filter. Time can pass more quickly than you realize, especially during busy seasons, and changing it on schedule will help prevent future shutdowns.
2. Inspect Your Furnace’s Outdoor Exhaust Pipes
Another issue we often see during heavy snow, strong winds, or extreme cold involves the exterior furnace exhaust and intake pipes. High-efficiency furnaces typically have two PVC pipes that exit through an exterior wall or roof. These pipes allow the furnace to bring in fresh air and exhaust combustion gases safely.
During a major snowfall or when drifts build up around the house, these pipes can become blocked. If they’re covered by snow, debris, or even leaves, your furnace can’t breathe — and it will shut itself off as a safety measure.
Take a moment to go outside and visually inspect these pipes. Check for:
- Snow accumulation or drifts
- Ice buildup
- Leaves, branches, or anything leaning against the pipes
- Roof-level pipes that may be buried after especially heavy snowfall
Clearing the blockage may allow your furnace to restart without needing a service technician.
3. Look for Furnace Flash Codes
Most modern furnaces are equipped with a diagnostic system that uses flashing lights or a small segment display to communicate error codes. These codes can often point directly to the source of the issue.
You’ll typically find a small sight glass or plastic viewing window on either the upper or lower section of the furnace cabinet. If your lights are on, it may be hard to see the flashing pattern — turning off the mechanical room light can help.
These flash codes aren’t always perfectly precise, but they can give both you and your HVAC technician a helpful starting point. In some cases, sharing the flash code with your heating contractor may allow them to diagnose the issue over the phone, saving you a service trip during a busy winter week.
When to Call a Professional
While these troubleshooting steps can solve many common cold-weather furnace problems, there are times when professional service is necessary. If your furnace continues to shut down, shows repeated error codes, or fails to restart after checking the filter and outdoor pipes, it’s best to contact a qualified HVAC technician. The issue may involve electrical components, sensors, pressure switches, or other internal systems that require specialized tools and training.
At Air Quality Mechanical, we understand how stressful it can be to lose heat during a Montana winter. Our team is here to provide fast, dependable service and help you keep your home warm and safe all season long.
If your furnace isn’t cooperating or if you’d like to schedule maintenance before the next cold snap hits, give us a call.
Stay warm, stay safe, and know we’re always here to help.