# Furnace not heating below freezing: safe checks first

> Furnace not heating below freezing in Pueblo? Walk through safe thermostat, breaker and filter checks, and learn which gas parts to leave to a contractor.

URL: https://puebloacrepair.com/furnace-not-heating-below-freezing/

# Furnace not heating below freezing: what to check in Pueblo

Published by Fieldstone Online

## What to check when a furnace stops heating in freezing weather

A furnace not heating below freezing usually comes down to a thermostat setting, a clogged filter, a tripped breaker or a safety switch that shut the system off. A homeowner can check each of those without special tools.

Gas parts, wiring and sealed components are a different matter. A licensed contractor works on those, and the safe checks end where those parts begin.

## Why does a cold night expose a weak furnace?

A furnace has the most to do when the outdoor air is coldest, so a weak part tends to give out then. The NOAA weather station near Pueblo records an average December to February daily low of 16.0°F, and it averages 152 days a year with a low of 32°F or below. A furnace that is already struggling has little room to hide in those temperatures.

Gas matters here too. About 78% of the 46,414 occupied homes in Pueblo are heated with utility gas, and a furnace that burns gas brings gas safety into every check you make.

What a contractor does once the checks run out is covered in [furnace repair in Pueblo](/furnace-repair/).

## Which safe checks come first?

Work from the easiest check to the hardest. Each one takes a few minutes, and none of them touches a gas part.

-   Thermostat: set the mode to heat and the target several degrees above the room reading. If the screen is dark, put in fresh batteries.
-   Breaker: find the furnace breaker in the panel. If it has tripped, reset it once.
-   Furnace switch: the switch on or near the furnace looks like a light switch, and a bumped one cuts all power.
-   Front panel: switch the furnace power off first, then press the front panel in until it seats fully. Many furnaces will not start unless a small door switch is pressed.
-   Filter: with the power off, slide the filter out and hold it up to a window.
-   Vents and returns: walk the house and look for a rug, couch or curtain covering a grille.

A clogged filter cuts airflow, and some furnaces shut the burner off when they run too hot. ENERGY STAR advises inspecting, cleaning or changing furnace filters once a month. It also says a dirty filter can increase energy costs and damage equipment, so the furnace may fail early.

## How do you tell the checks worked?

Turn the power back on and give the furnace time to run through its start sequence. You should hear the inducer fan, then the burner, and then the blower pushes warm air out of the vents.

Hold a hand over a vent in the room farthest from the furnace. Warm air there, and a house that climbs toward the thermostat setting, means the cause was a setting, a filter or a switch.

Stop if the breaker trips again, if the burner lights and then goes out, or if the air stays cold after the blower runs for a while. Repeating the same restart will not fix a failed part.

## What do ignition and flame sensor symptoms mean?

A typical gas furnace starts in steps. The thermostat calls for heat, the inducer fan clears the burner area, the igniter warms up, the gas valve opens, and a flame sensor confirms that a flame is burning. If the sensor does not see the flame, the control shuts the gas off to stay safe.

That sequence explains a furnace that lights for a short burn and then drops out. A dirty flame sensor, a weak igniter or a venting problem can each cause it. You cannot tell which from the living room.

Clicking with no flame, a burner that never tries to light and a furnace that cycles on and off all point the same direction. The cause sits beside the burner and the gas valve, which is contractor work. For a closer look at what is examined, see [what a furnace repair visit looks at](/what-happens-during-furnace-repair-visit/).

## What should you never do with the gas parts?

Leave the burner, the gas valve, the igniter and the sensor to a licensed contractor. Wiring and the control board belong on that list as well.

-   Do not take apart the burner area or pull the valve.
-   Do not tape down, jump or bypass a safety switch to keep the furnace running.
-   Do not poke at the sensor or the igniter with a tool.
-   Do not run the furnace with the front panel off.

A licensed contractor tests the safety switches, checks the ignition parts and the wiring, and cleans or replaces what has failed. Those steps need meters and an understanding of how the gas train is built.

If you smell gas, leave the house, then call the gas utility from outside.

If a carbon monoxide alarm sounds, get everyone out and call emergency services.

## When is it time to stop and call a contractor?

Call once the safe checks are done and the house is still cold. Call sooner if you notice any of these:

-   A breaker that trips again after the one reset.
-   A burning smell, banging or a new squeal when the furnace runs.
-   Water pooling around the furnace.
-   A furnace that lights and drops out again and again.

Jot down what the thermostat says, what the furnace does when it tries to start, any sounds, and the checks you already made. Those notes make the repair conversation shorter and clearer.

## Next step: furnace repair when the checks run out

If the thermostat, breaker, filter and vents are all in order and the house still will not warm, the problem is likely inside the furnace. That is work for a licensed contractor.

Read [how furnace repair works in Pueblo](/furnace-repair/) to see what the work involves and how the phone line fits in.

 ![Homeowner's hand pulling a pleated filter from a closed gas furnace](/pics/a54e8c2960-800.webp)

## More on furnace repair

Checks that do not bring the heat back lead to a repair, and the repair page explains how that works.

[furnace repair in Pueblo](/furnace-repair/)

## Questions about a furnace that will not heat

-   ### Why does my furnace blow cold air when the house is freezing?
    
    Often the cause is a setting, a clogged filter or a safety shutoff that stopped the burner while the blower kept running. Check the thermostat mode and the filter first. If the air stays cold, a licensed contractor looks at the ignition parts.
    
-   ### Can I keep flipping the furnace breaker back on?
    
    Reset it one time, and only if it has tripped. A breaker that trips again points to an electrical fault, and a licensed contractor checks the wiring and the furnace's electrical parts.
    
-   ### Can I clean the flame sensor myself?
    
    Reaching the sensor means working beside the burner and the gas valve. That is contractor work, so leave it alone and note what the furnace does when it tries to light.
    
-   ### How often should I change the furnace filter?
    
    Look at it often, and change it when you can no longer see light through the pleats. The contractor advises on how often your particular system needs a new one.
    
-   ### Who confirms availability and fees after I call?
    
    Each independent contractor confirms its own fees. The line only connects the call where a contractor is available, and nothing about the call is promised. Service availability and appointment times depend on the independent contractor, who confirms them when you call.
    

 ![Homeowner's hand changing batteries in a hallway wall thermostat](/pics/23eb24b853-800.webp)

## Call about furnace repair when the checks fall short

Tap the call button to reach a phone line that connects callers with licensed, insured independent contractors. Keep your notes on the thermostat and the furnace's behavior within reach.

An automated prompt may ask for your ZIP code and the service you need. Where a contractor is available, the line connects the call to that contractor, who then confirms availability. Nothing about the call is promised, not a ZIP code, a connection or an answer.

Each independent contractor confirms its own fees. Service availability and appointment times depend on the independent contractor.

We connect you with a licensed, insured HVAC contractor.

[Call about furnace repair availability. (719) 225-2602](tel:+17192252602)

## Sources

-   [US Census Bureau](https://data.census.gov/table/ACSDT5Y2024.B25040?g=1600000US0862000), checked 2026-11-09
-   [NOAA National Centers for Environmental Information](https://www.ncei.noaa.gov/data/normals-annualseasonal/1991-2020/access/USC00058992.csv), checked 2026-11-09
-   [ENERGY STAR](https://www.energystar.gov/saveathome/heating-cooling/maintenance-checklist), checked 2026-11-09