Why is my furnace blowing cold air in Severance

A furnace blowing cold air in Severance CO almost always means one of three things: the burner never lit, the blower is running before the heat exchanger warms up, or the thermostat is calling for fan-only mode. In most homes we service around Severance, the fix is a failed igniter, a dirty flame sensor, or a thermostat set to ON instead of AUTO. The rest of this post walks through the causes in the order we actually check them, plus what you can safely test yourself and what should stay in a technician's hands.

Why your furnace is blowing cold air in Severance CO

A furnace blowing cold air in Severance CO is a category of airflow problem where the blower moves air across a heat exchanger that is not hot enough to warm it. That definition matters because it tells you where to look: the flame side, the airflow side, or the controls telling both what to do.

Your furnace has a fixed sequence. The thermostat calls for heat. The draft inducer spins up. The ignition source lights the burners. The flame sensor confirms fire. Only then does the blower kick on and push air across the heat exchanger. Break any step in that chain and you get the same symptom - a fan running, air moving, and no heat in it.

Severance sits at roughly 5,000 feet, and that thin air changes how gas appliances behave. We see more ignition and flame-sensor faults here than techs at lower elevations report, because the air-to-gas mix that worked at the factory is slightly off at altitude. Add a Weld County winter that routinely drops into the single digits, and a furnace that is 80 percent healthy in October becomes a cold-air machine by January.

If you want the full picture of what our team handles, Furnace Repair Severance CO covers diagnostics, parts, and same-day service across the area.

Quick checks before you call anyone

Run these five checks before you pick up the phone. About one in four cold-air calls we run in Severance ends with the homeowner finding the problem in this list.

1. Thermostat mode. If the fan switch is set to ON instead of AUTO, the blower runs continuously and pushes room-temperature air. Set it to AUTO and give it 10 minutes.
2. Filter. A filter loaded past about 70 percent restriction chokes airflow and can trip the high-limit switch, which shuts the burners off while the fan keeps running. Hold it up to a light - if you cannot see through it, replace it.
3. Breaker and service switch. Check the breaker at the panel and the toggle switch on or near the furnace. Both get flipped during summer AC work and never flipped back.
4. Gas valve. Confirm the shutoff valve on the gas line to the furnace is parallel to the pipe, not perpendicular.
5. Error code. Most furnaces built after 2010 have a blinking LED on the control board. Count the flashes and look up the code on the door panel chart.

If none of that changes anything, the problem is inside the cabinet and you need a technician. Our heater repair Severance techs carry igniters, flame sensors, and control boards on the truck so most cold-air calls are one-visit fixes.

What causes a furnace to blow cold air in Severance Colorado

What causes a furnace to blow cold air in Severance Colorado comes down to a short list of failures, and they show up in a predictable order of frequency. Here is what we actually find on calls.

Failed hot surface igniter

The igniter is a ceramic element that glows orange to light the gas. It cracks from thermal cycling, and at altitude it runs hotter and fails faster. A cracked igniter is the single most common cold-air cause we see - roughly 30 percent of our winter calls. Replacement runs $180 to $320 in 2026 pricing, parts and labor.

Dirty or failed flame sensor

The flame sensor is a metal rod in the burner flame. It sends a microamp signal back to the board confirming fire. A film of carbon blocks that signal, the board thinks the burners never lit, and it shuts the gas off within 5 to 7 seconds while the blower keeps running. Cleaning it takes 10 minutes; replacing it runs $120 to $220.

Thermostat set to fan-only

Free to fix, easy to miss. If the fan switch reads ON, the blower runs 24/7 regardless of heat demand. This is the number one cause of "my furnace is blowing cold air" calls that turn out to be nothing.

Tripped high-limit switch

The high-limit is a safety that cuts the burners when the heat exchanger gets too hot. A clogged filter, blocked return, or closed register causes it to trip. The fan keeps running to cool the exchanger, so you feel cold air. Fix the airflow restriction and the switch resets.

Bad control board or blower relay

When the board stops sending the signal to the gas valve, the blower runs but the burners never fire. We diagnose this with a multimeter at the valve terminals. Board replacement runs $450 to $850 depending on the model.

Pilot light out on older furnaces

Standing-pilot furnaces built before 1990 still exist in some older Severance and Eaton homes. If the pilot is out, the burners never light. A pilot light relight Severance visit is quick, but if the pilot keeps going out, the thermocouple or gas valve is the real problem.

Heat exchanger crack

The serious one. A cracked heat exchanger leaks combustion gas into your supply air and can also cause the flame to roll out and trip the limit. If we find a crack, we stop and talk to you about replacement rather than repair - it is a carbon monoxide risk, not a performance issue.

How do I fix a furnace blowing cold air in Severance

How do I fix a furnace blowing cold air in Severance depends on which part of the sequence failed. The flowchart below is what our techs run in the field.

• Fan runs, no flame, no error code: check gas valve, then thermostat call for heat, then control board signal to the gas valve.
• Fan runs, igniter glows, no flame: gas supply issue or failed gas valve. Call a pro - do not open the gas train yourself.
• Flame lights then dies in 5-7 seconds: flame sensor. Clean or replace.
• Flame lights, runs 2-5 minutes, then shuts off with fan still on: high-limit trip from airflow restriction. Filter, return, or blower wheel.
• Fan runs constantly, no heat call: thermostat fan switch on ON, or a stuck blower relay on the board.

Two of those five you can fix yourself. The other three involve gas or line voltage and should not be touched without a meter and the right training. If you are not sure which bucket you are in, our blower fan repair Severance team can diagnose it in one visit - blower problems and cold-air complaints overlap more than people expect.

Common mistakes we see in Severance homes

We see the same four mistakes over and over on cold-air calls in Severance, and each one either wastes money or creates a safety problem.

Replacing the thermostat first. Homeowners swap a $200 smart thermostat hoping it fixes the cold air. It almost never does. The thermostat is rarely the failed part on a cold-air call - maybe 5 percent of the time.

Running the furnace with a cracked heat exchanger. If you smell combustion or your CO detector has chirped, shut the furnace off at the breaker and call us. Do not run it "just until morning."

Using the wrong filter. A MERV 13 filter in a system designed for MERV 8 chokes airflow and trips the high-limit within a week. Match the filter to the furnace's rated static pressure, not to the highest number on the shelf.

Skipping fall maintenance. A $99 to $149 furnace checkup Severance in September catches the igniter and flame sensor issues that would have stranded you in January. We see maybe one in five Severance homeowners actually book it.

When to call a professional

Call a professional the moment you smell gas, hear a repeated clicking with no ignition, see a CO detector alarm, or find a puddle or soot around the furnace. Those are not DIY symptoms.

For everything else, if you have run the five quick checks and the air is still cold after 15 minutes, the problem is inside the cabinet. Our team at Severance Furnace Repair Pros handles gas, propane, and electric furnaces across Severance, and we carry the common parts so most cold-air calls are fixed the same day. We also serve the surrounding towns - homeowners in Furnace Repair in Windsor and Furnace Repair in Eaton get the same diagnostic process and the same parts inventory.

Frequently Asked Questions

Why is my furnace blowing cold air in Severance CO?

The most common causes are a failed igniter, a dirty flame sensor, a thermostat set to fan-only, or a tripped high-limit switch from restricted airflow. At Severance's 5,000-foot elevation, ignition components fail faster than at lower altitudes, so igniter and flame-sensor faults lead the list.

How do I fix a furnace blowing cold air in Severance?

Set the thermostat fan switch to AUTO, replace a clogged filter, confirm the breaker and gas valve are on, then check the LED error code. If the burners still do not light within 15 minutes, the issue is inside the cabinet and needs a technician with a multimeter.

Should I call a pro for furnace blowing cold air in Severance?

Yes, if you smell gas, hear clicking with no flame, see a CO alarm, or the burners will not light after basic checks. Gas train and line-voltage work is not a homeowner repair. Most cold-air calls we run are one-visit fixes with parts we stock on the truck.

What causes a furnace to blow cold air in Severance Colorado?

In Severance specifically, altitude-related ignition faults, dust from new construction, and hard temperature swings between day and night drive most cold-air calls. The mechanical causes are the same as anywhere - igniter, flame sensor, limit switch, control board, or heat exchanger - but the frequency skews toward ignition.

How much does it cost to fix a furnace blowing cold air in Severance?

Typical 2026 repairs run $120 to $320 for a flame sensor or igniter, $450 to $850 for a control board, and $1,800 to $4,500 for a heat exchanger replacement. Diagnostic fees in the Severance area run $79 to $129 and are usually credited toward the repair.

Get help with Furnace Repair in Severance

If your furnace is blowing cold air and the quick checks did not solve it, we can be at your door today. Call Severance Furnace Repair Pros at (970) 1234567 and we will diagnose it, quote the repair upfront, and get heat back into your house.