Why Won’t My Rheem Furnace Ignite—and Is There Anything I Can Safely Check Before Calling in a Technician?
If your Rheem furnace isn’t igniting, you’re likely dealing with a cold house, rising energy bills, or no heat at all. It’s a frustrating and uncomfortable situation, especially in the middle of winter.
At Honest Fix, we’ve helped hundreds of homeowners troubleshoot furnace ignition issues. Alex Largent, owner of Honest Fix and a 20-year veteran technician and installer, has personally handled ignition problems on everything from older Rheem units to new high-efficiency systems.
In this guide, we’ll break down the most common reasons a Rheem furnace won’t ignite. These are safe, simple checks you can do yourself before calling in a professional.
1. Check the Thermostat First
Make sure your thermostat is set to “heat,” and that the temperature setting is above the current room temperature. It may sound basic, but Alex recalls a call where a furnace “wouldn’t turn on”—only to find out the thermostat had been accidentally set to “cool” by a curious toddler.
2. Power Supply Issues
Ensure your furnace has power. Check the circuit breaker and the furnace switch (usually located on or near the unit). A tripped breaker or turned-off switch is often to blame. Alex once found a flipped switch that had been mistaken for a light switch.
3. Furnace Door Safety Switch
Rheem furnaces have a safety switch that prevents operation when the access panel isn’t properly closed. Make sure the door is securely latched. This small oversight once left a family without heat overnight.
4. Dirty Flame Sensor
A dirty flame sensor can prevent ignition. If your furnace clicks on but shuts down quickly, this might be the culprit. Cleaning it requires shutting off power and gently wiping the sensor with steel wool. If you’re unsure, it’s best to call a professional.
5. Ignitor Problems
The ignitor might be cracked or faulty. This is common in older units. Alex once replaced a cracked ignitor in a Rheem Classic 90 Plus. The homeowner had no idea this small part was the root cause of the problem.
6. Gas Supply Issues
Ensure the gas valve to the furnace is open. If other gas appliances aren’t working either, the issue may be with your utility provider. Never attempt to repair gas lines yourself.
7. Clogged Air Filter
A severely clogged filter can restrict airflow, triggering safety shutoffs. Change the filter and see if the system restarts. This quick fix has saved many Honest Fix customers from unnecessary service calls.
When to Call Honest Fix
If you’ve checked all the above and your furnace still won’t ignite, it’s time for a professional inspection. You may be dealing with a control board issue, pressure switch malfunction, or another fault.
We offer fast, honest service. Our licensed Comfort Guides will explain what went wrong, how we’ll fix it, and what it will cost—upfront. (Free exact quotes apply to new system installations only.)
Most ignition problems can be traced to a few common issues you can check yourself. By understanding what to look for, you can save time, avoid unnecessary costs, and know when it’s time to call in the pros. And when you do, we’re here to help—especially if you live near Steubenville, Ohio.
