ICP Furnace Blowing Cold Air

ICP Furnace Blowing Cold Air — How to Troubleshoot and Fix It

When your ICP gas furnace is blowing cold air instead of heat, it usually means one of three key components isn’t working as it should. The most common causes are:

1. A dirty air filter
2. A failed interlock switch
3. A bad igniter

Let’s go through each issue and how to troubleshoot it safely.

1. Dirty Air Filter

A dirty or clogged air filter is one of the most frequent reasons a ICP furnace stops heating.

The filter’s job is to catch dust and debris before they reach the blower and heat exchanger. But when it gets packed with buildup, it chokes off airflow through the system.

How a dirty air filter keeps your furnace from heating

• The restricted airflow makes the heat exchanger run too hot.
• When the heat exchanger overheats, the furnace’s limit switch turns off the burners to prevent damage.
• With the burners off, the blower keeps running, so you feel cool (or barely warm) air coming from your vents instead of heat.

How to check and replace the furnace air filter

1. Turn off power to the furnace at the switch or breaker.
2. Locate the filter—usually behind a panel near the blower compartment or in the return air vent.
3. Slide out the old filter and check it against a light source. If you can’t see light through it, it’s too dirty.
4. Replace it with a new filter of the same size and airflow rating.
5. Restore power and turn the furnace back on.

A clean filter allows proper airflow and ensures your furnace can heat efficiently again.

2. Failed Interlock Switch

Modern ICP furnaces include several interlock or safety switches that prevent unsafe operation. Common examples include:

• Blower door switch — ensures the access panel is properly closed before the furnace starts.
• Pressure switch — verifies proper venting and airflow through the combustion system.
• Limit switch — shuts off burners if the furnace overheats.

Why a failed interlock switch prevents heating

If any interlock switch fails or doesn’t close properly, the furnace’s control board won’t allow the ignition sequence to start. The blower may still run, but the burners won’t light—resulting in cold air from your vents.

An HVAC technician can use a multimeter to test each switch for continuity and replace any that have failed.

3. Bad Igniter

The igniter is what lights the gas burners. Most modern furnaces use a hot surface igniter that glows red-hot to ignite the gas as it flows into the burner assembly.

Why a failed igniter stops the furnace from heating

If the igniter is cracked, weak, or has lost electrical continuity, it won’t get hot enough to light the gas.

When the control board detects this failure, it shuts off the gas valve to prevent unburned gas from building up.

The result: no heat.

A trained furnace technician can test the igniter for resistance and replace it if it’s defective.

Why Choose Sears Home Services for ICP Furnace Repair

When your ICP furnace blows cold air, Sears Home Services is your trusted source for professional repair.

Our licensed technicians service all ICP furnace models and carry the part to fix heating problems fast.

We provide nationwide coverage, with local HVAC repair experts in major metro areas including:

• Seattle
• Minneapolis–St. Paul
• Washington, D.C.
• Philadelphia
• New York City
• Chicago
• Dallas–Fort Worth
• Houston
• Los Angeles
• Miami
• Atlanta
• Denver
• Phoenix

Whether you’re dealing with a safety switch failure, bad igniter or any other furnace failure, our experts can diagnose and repair your heating system quickly—keeping your home comfortable and your ICP furnace running safely.

Schedule Furnace Repair Today

Don’t wait for the temperature to drop further. Schedule furnace repair with Sears Home Services today and get your ICP heating system working right again.