If your Rheem furnace is suddenly blowing cold air, you’re likely feeling confused, frustrated, and maybe even worried about an expensive repair. You’re not alone. As a Rheem Pro Partner and a 20-year HVAC veteran serving the Steubenville, Ohio area, I’ve worked on hundreds of Rheem systems. When homeowners call us with this issue, it’s almost always one of a handful of common causes—and in many cases, it’s something that can be fixed without major expense.
In this article, I’ll walk you through the most frequent reasons your Rheem furnace might be pushing out cold air, how to identify each issue, and when it’s time to call in a pro. Whether you’re troubleshooting a Rheem furnace blowing cold air but fan is running, or wondering why your Rheem furnace is not heating, this guide is designed to help.
1. Your Thermostat Settings Might Be Off
Why it happens: If your thermostat is set to “On” instead of “Auto,” the fan will run continuously—even when the furnace isn’t producing heat.
How to check: Make sure your thermostat is set to “Auto.” This way, the fan only runs when the furnace is actively heating.
When to call a pro: If your thermostat settings are correct but the issue persists, there could be a wiring issue or a faulty thermostat.
2. The Furnace Is Overheating and Tripping a Safety Limit
Why it happens: A dirty air filter or blocked vents can cause your furnace to overheat. When that happens, the safety limit switch shuts down the burners, but the fan continues to blow to cool down the unit.
How to check: Inspect your air filter. If it’s dirty, replace it and see if the problem resolves. Also, make sure your vents aren’t blocked by furniture or rugs.
When to call a pro: If a new filter doesn’t fix the issue, your system might have internal buildup or a faulty limit switch.
3. The Ignitor or Flame Sensor Is Faulty
Why it happens: Rheem furnaces use a hot surface ignitor to light the burners. If it’s damaged or the flame sensor is dirty, the burners may shut off shortly after ignition, leaving the fan running.
How to check: You might hear a click followed by nothing. If your furnace lights briefly then shuts down, this is a likely culprit.
When to call a pro: These parts are sensitive and should be diagnosed and replaced by a licensed technician.
4. Your Condensate Drain Line Is Clogged
Why it happens: High-efficiency Rheem furnaces produce condensation. If the drain line clogs, it can trigger a shutdown to prevent water damage.
How to check: Look near the base of your furnace for any standing water or slow drainage.
When to call a pro: If there’s visible water or you hear gurgling, it’s time to get it cleared and inspected.
5. You’ve Got a Control Board, Error Code, or Sensor Issue
Why it happens: If your system is giving you fault codes or acting erratically, the issue could stem from the main control board or sensors like the pressure switch.
How to check: Rheem furnaces typically have a blinking LED light. Count the flashes and look up the code in your manual. Understanding Rheem diagnostic codes can provide clues to internal malfunctions, especially when your furnace is blowing cold air but not heating.
When to call a pro: If you’re seeing error codes or nothing seems to help, the issue could be electrical or mechanical and needs professional attention.
Troubleshooting: Rheem Furnace Blows Cold Air But Fan Is Running
This is one of the most common complaints we get in the winter months. If your fan keeps blowing but no heat is coming out, start by checking:
- Thermostat setting (should be on “Auto”)
- Filter condition
- Ignitor and flame sensor activity
- Condensate drain for clogs
- Error codes or blinking lights on the control panel
If you’ve checked those and still have no heat, it’s time to call a licensed tech.
Real Story From the Field: A Wintersville Wake-Up Call
Last December, I got a call at 6:30 AM from a homeowner in Wintersville. Her Rheem Classic Plus furnace was blowing cold air during one of the coldest mornings of the year. She had just replaced the filter but didn’t realize her flame sensor was coated in residue from a summer of inactivity. We cleaned the sensor and had the system heating again in under 30 minutes. A full-blown emergency averted—and no parts needed.
Bottom Line
There are a handful of common reasons your Rheem furnace might be blowing cold air, ranging from simple thermostat missettings to component failure. Many are minor and easy to fix. But if you’ve checked the basics and still have no heat, don’t wait. Get a licensed HVAC professional to diagnose the issue before it becomes more serious.
At Honest Fix, we offer fast, expert diagnosis and repairs for all Rheem furnace models. If you’re within 15 miles of Steubenville, Ohio, call us anytime to schedule a service call.
