Furnace Not Heating? 8 Things to Check Before Calling

When your furnace stops heating, it can be stressful—especially during cold weather. Before calling for service, there are several things you can check yourself that might resolve the issue or help you understand what is happening.

1. Check Your Thermostat

This might seem obvious, but thermostat issues are one of the most common causes of heating problems.

**What to check:**

• Ensure the thermostat is set to "Heat" mode, not "Cool" or "Off"
• Verify the temperature is set higher than the current room temperature
• Check that the fan setting is on "Auto" rather than "On" (constant fan can make air feel cool)
• Replace batteries if your thermostat uses them
• Make sure nothing is blocking the thermostat sensor

2. Check the Power

Furnaces need electricity even if they use gas for heat.

**What to check:**

• Look for a power switch near the furnace—it looks like a light switch and can be accidentally turned off
• Check your electrical panel for a tripped breaker labeled "Furnace" or "HVAC"
• If the breaker has tripped, reset it once. If it trips again, do not keep resetting—this indicates an electrical problem requiring professional attention

3. Check the Air Filter

A severely clogged filter can cause the furnace to overheat and shut down for safety.

**What to check:**

• Locate your filter (usually in the return air duct or at the furnace)
• Hold it up to light—if you cannot see through it, it needs replacement
• Replace with a new filter of the same size and type

4. Check the Pilot Light (Older Furnaces)

If you have an older furnace with a standing pilot light:

**What to check:**

• Look through the small window or access panel for a flame
• If the pilot is out, follow the manufacturer's instructions to relight it
• If it will not stay lit, the thermocouple may need replacement

5. Check for Blocked Vents

Restricted airflow can cause heating problems.

**What to check:**

• Walk through your home and ensure all supply vents are open
• Check that nothing is blocking return air vents (furniture, curtains, rugs)
• Make sure the furnace area has adequate clearance

6. Check the Gas Supply

If you have a gas furnace:

**What to check:**

• Ensure the gas valve to the furnace is in the "On" position
• Check if other gas appliances are working (stove, water heater)
• If you smell gas, leave immediately and call your gas company

7. Check the Condensate Drain (High-Efficiency Furnaces)

High-efficiency furnaces produce condensation that must drain properly.

**What to check:**

• Look for a small drain line and trap near the furnace
• Check if the drain is clogged or the trap is full
• Clear any visible blockages carefully

8. Reset the Furnace

Many furnaces have a reset function:

**What to try:**

• Turn off power to the furnace for 30 seconds, then restore power
• Some furnaces have a reset button on or near the unit

When to Call a Professional

Call for service if:

• You smell gas or burning
• The furnace makes unusual sounds (banging, screeching, grinding)
• You have tried the above steps with no improvement
• The problem keeps recurring
• Your furnace is cycling on and off rapidly
• You see cracks in the heat exchanger
• The pilot light is yellow instead of blue

Some issues require professional tools and expertise to diagnose and repair safely. If you are unsure, it is always better to call for an assessment.