Call (719) 670-8043
Menu

Furnace runs, air isn’t warm

Furnace Blowing Cold Air in Pueblo?

Cold air from the vents almost always comes down to one of four things: the fan setting, an overheating shutdown, burners that won’t light or stay lit, or a blocked drain on a high-efficiency furnace.

Call (719) 670-8043 Match your pattern

24/7 · Licensed & insured · Pueblo & Pueblo West

Metal heating register set into a hardwood floor

Here’s how to tell which — and when to call us.

Start with the pattern

NormalCool for the first minute, then warm

That’s air that was sitting in the ductwork. Nothing to fix.

Easy fixRoom-temperature air between heating cycles

The thermostat fan is set to ON instead of AUTO, so the blower runs nonstop. Switch it to AUTO.

Check, then callWarm at first, then cold while the blower keeps going

The furnace overheated and the high-limit switch shut the burners off. Usually a clogged filter or blocked vents. Change the filter; if it keeps happening, call us.

Call usNever warm at all

The burners aren’t lighting, or they light and quit. The usual suspects: a dirty flame sensor, a failed igniter, a pressure switch held open by a blocked vent, a clogged condensate drain, a pilot that’s out on an older furnace, or a gas supply problem.

StopCold air and a gas smell, a CO alarm, or soot around the furnace

Turn it off and get outside. See the safety steps below.

What you can safely check

  1. Fan to AUTO

    Then give the furnace a full cycle to see whether the cold air stops.

  2. The filter

    ENERGY STAR recommends checking it monthly in heating season and changing it at least every three months. A clogged one is the classic cause of overheating shutdowns.

  3. Registers and returns

    Open the supply registers and move furniture or rugs off the return grilles.

  4. Vent pipes outside

    On a high-efficiency furnace, clear snow or ice from the plastic intake and exhaust pipes on the outside wall.

  5. The blinking light

    Count the flashes on the control board light and match them to the code chart on the furnace door, or tell us the pattern when you call.

Two Pueblo-specific causes we see

Snow over the side-wall vents

High-efficiency furnaces pull in air and push out exhaust through plastic pipes, often on a side wall. A pressure switch confirms that air is moving before the burners are allowed to light. When snow or ice blocks those pipes, the switch stays open and the burners stay off. Pueblo’s normal snowfall is about 28 inches a season, and the record season brought 69.6 inches (1989–90). Trane’s guidance is to keep the vent openings at least 12 inches above the snow level you normally expect — if a drift reaches yours every winter, the venting may need to be raised.

A flame that isn’t set up for 4,700 feet

Pueblo’s thin air changes how gas burns. A furnace that wasn’t adjusted for altitude can burn rich and sooty (ACHR News), and residue on the flame sensor is a classic reason a furnace lights for a few seconds and then shuts off. A good repair cleans or replaces the sensor and checks that the gas input matches the altitude table in your furnace’s manual.

What we repair

Depending on what the diagnosis finds, the fix might be cleaning or replacing the flame sensor, replacing a failed hot-surface igniter, replacing a limit switch worn out by repeated overheating (and fixing the airflow problem behind it), clearing or replacing pressure-switch tubing or a condensate trap, or correcting venting that keeps getting blocked.

Typical U.S. range to replace a flame sensor: $80–$250, per HomeGuide, Nov 2026. That’s a national range, not a Pueblo quote — you get the exact price after diagnosis.

Questions we hear

Why does my furnace blow warm air, then cold air, while the fan keeps running?

That pattern usually means the furnace overheated and its high-limit switch shut the burners off as a safety measure, while the blower kept running to cool things down. The most common reason is restricted airflow — a clogged filter, closed registers or blocked return vents. If a clean filter doesn’t fix it, call us: repeated overheating can wear out the limit switch, and it can point to bigger problems.

Should my thermostat fan be set to ON or AUTO?

For heating, AUTO. On AUTO the blower runs only while the furnace is heating. On ON it runs all the time, so between heating cycles it pushes room-temperature air through the vents — which feels cold. Carrier calls this the most common reason people think their furnace is blowing cold air.

Is a little cool air at startup normal?

Yes. A brief puff of cooler air when the blower first starts is normal — it’s the air that was sitting in the ducts. It should turn warm within a minute or so.

Can I clean the flame sensor myself?

Manufacturers disagree. Carrier describes lightly cleaning it; Trane says to leave it to a technician. It means shutting off power and gas and removing a part from the burner area, so if that isn’t something you’re comfortable with, call us. Never bypass or disconnect it — it’s what keeps gas from flowing when there’s no flame.

I have a heat pump, not a furnace. Is cold air normal?

During a defrost cycle, yes — briefly. The outdoor unit may give off a cloud of steam and the indoor air can feel cool for a few minutes. Constant cold air isn’t normal. See heat pump repair.

Still blowing cold? Call us.

We answer 24/7 for Pueblo and Pueblo West. Our licensed & insured technicians find what’s keeping the burners off and tell you the price before any work starts.

Call (719) 670-8043
Where the Pueblo facts on this page come from

Checked against these public sources on November 3, 2026. Weather figures are National Weather Service records for Pueblo Memorial Airport.

Call (719) 670-8043