How Long Does a Furnace Limit Switch Take to Reset (and What to Do If It Doesn't)

A furnace limit switch typically resets on its own within 30 minutes to an hour once the furnace cools down. If it’s been longer than that and your furnace still won’t fire, the switch either didn’t reset, has failed permanently, or the thing that caused it to trip is still happening.

What the Limit Switch Actually Does

The limit switch is a safety device mounted near the heat exchanger, on the plenum or partition panel. It shuts the burner off if the furnace gets too hot. When everything’s working right, you’d never know it’s there. When it trips, your furnace starts short-cycling (fires, shuts off quickly, fires again) or just won’t stay on.

Most limit switches have a small manual reset button, often red. Pressing reset without fixing the underlying cause just trips it again, sometimes faster each time.

Why It Tripped (in Order of Likelihood)

Restricted airflow is the most common cause by a wide margin. Pull your air filter out and look at it. If it’s been more than a month, that’s probably your problem. Walk the house and make sure every supply and return vent is open and clear. Blocked registers cut airflow the same as a dirty filter.

A dirty blower wheel comes next. The fan can accumulate enough debris over years that airflow drops significantly even with a clean filter. Cleaning it is a maintenance job a technician does.

A cracked heat exchanger. Take this one seriously. A cracked heat exchanger can let combustion gases leak into your living space. If your furnace is older (15-plus years) and keeps tripping even with good airflow, this is on the diagnostic list. Don’t keep resetting and running it until a technician rules it out.

A failed limit switch itself. The switch can fail open or closed. It’s an inexpensive part, but the diagnosis requires a multimeter and a thermocouple probe, not guessing.

Flue or exhaust problems. A blocked flue causes overheating. Less common, but relevant if the furnace is in a tight mechanical room or shares a chimney.

What You Can Check Yourself

Three things are safe to do before calling: replace the filter if it’s dirty, open any closed vents, and press the reset button on the limit switch once. If the furnace fires and runs a full cycle, keep an eye on it. If it trips again, stop resetting it.

Working inside the blower compartment, testing the heat exchanger, or diagnosing electrical faults needs proper tools and training. Repeated resets without a diagnosis can turn a smaller fix into a much larger one.

What a Tech Actually Diagnoses

On a limit switch call, we’re not just pressing the button. We measure temperature rise across the heat exchanger (supply vs. return air), check static pressure, inspect the blower, and often pull the burner assembly to look at the heat exchanger. Temperature rise alone tells you a lot: if it’s running too high, the furnace is fighting restricted airflow somewhere.

We also test whether the switch trips at its rated temperature or below it. That tells us if the switch itself is failing. These aren’t things you can determine by eye.

When to Call Us

If the switch trips more than once after a reset, or you can’t find an obvious airflow problem, get a technician in. Same goes if the furnace is older, or if there’s any doubt about the heat exchanger. Running a furnace with a cracked heat exchanger isn’t a risk worth taking.

Bay Area heating season runs hard November through March. A limit switch that keeps tripping usually means something else is wearing out too. Catching it early is cheaper than catching it mid-January.

We cover furnace diagnostics, limit switch replacement, heat exchanger inspection, and blower cleaning across the Bay Area. Same or next-day appointments are usually available. Call us at (925) 999-4095 or book at bayareahvacservice.com.

Key takeaways

• A limit switch typically resets on its own within 30 to 60 minutes after the furnace cools down.
• A clogged air filter is the most common cause of a tripping limit switch, check it first.
• If the switch trips again after a manual reset, stop resetting it and get a technician to diagnose the root cause.
• A cracked heat exchanger can also trigger the limit switch and is a safety issue that needs professional inspection.

Related questions

Written by Andrew Kuznetsov. Andrew is the founder and owner of Bay Area HVAC Service (ADRIUM Service Solutions). He holds a California Contractor License (CSLB #1136642), EPA 608 certification, and completed factory training at the Daikin/Goodman plant in Houston in 2025. He writes from direct field experience, not marketing copy.

Further reading

• Mitsubishi Hyper-Heat (H2i): How It Keeps Putting Out Heat When It Gets Cold in the Bay Area , Most people think heat pumps quit when it gets cold. Mitsubishi's Hyper-Heat (H2i) line is built to keep working as temperatures drop, which matters more here than folks expect, especially on cold mornings and up in the East Bay hills.
• Mitsubishi Mini-Split Blinking a Fault Light? What It Means and What to Do , A blinking light on your Mitsubishi indoor head is the system telling you something is wrong. Here is what the blink pattern means, the checks you can safely do yourself, and when to bring in a factory-trained tech.
• Why Your Mitsubishi Mini-Split Is Leaking Water Inside (and How to Fix It) , A Mitsubishi mini-split dripping water inside almost always comes down to condensate that can't drain. Here's what causes it, the safe checks you can do yourself, and when to call a tech.