Furnace Not Turning On? Troubleshoot Before You Call

A furnace that won't start on a cold night is stressful — but the fix is sometimes something you can handle in a few minutes. Work through these checks first (safely), and if it still won't run, we're here 24/7.

Safety first: if you ever smell gas (a rotten-egg odor), don't touch switches or troubleshoot — leave the home and call your gas utility, then us, from outside.

1. Check the thermostat

Set it to HEAT and raise the temperature a few degrees above the current room temp. Replace the batteries if it's battery-powered — dead batteries are a surprisingly common cause.

2. Check the power

Look for a tripped breaker labeled for the furnace and reset it. Many furnaces also have a standard light-switch-style power switch nearby (often at the top of the basement stairs or on the unit) — make sure it's ON.

3. Check the air filter

A severely clogged filter can trigger a safety shutoff. If it's filthy, replace it and try again.

4. Check the furnace door panel

Most furnaces won't run if the front access panel isn't fully seated — there's a safety switch behind it. Make sure it's closed firmly.

5. Check the condensate drain

High-efficiency furnaces shut down if the condensate line clogs and the safety float trips. If you see standing water near the unit, that may be the cause.

When to call a professional

If you've checked all of the above and your furnace still won't fire — or you're dealing with a pilot/ignitor or gas-valve issue — leave it to a licensed technician. Lumen offers 24/7 emergency heating repair across Philadelphia and the suburbs. Call (267) 252-2969 any time.