Why Is My Furnace Not Turning On? (8 Reasons and What to Do About Them)

You Just Turned Your Thermostat Up and Nothing Happened

The temperature in your house is dropping, you can see your breath when you exhale, and you just realized your furnace isn't turning on. You adjust the thermostat again. Still nothing. No warm air, no familiar sound of the blower starting up, just silence and a house that's getting colder by the minute.

If this is happening to you right now, you're probably feeling a mix of panic and frustration. In Rochester, a non-working furnace isn't just an inconvenience - it's an emergency, especially if temperatures are below freezing and you have kids, elderly family members, or pets in the house.

Before you panic completely, here's some good news: many furnace problems that prevent startup are actually simple fixes you might be able to handle yourself. Others require professional help, but knowing what's wrong helps you understand whether you're dealing with a quick repair or something more serious.

Let's walk through the most common reasons furnaces don't turn on, starting with the simplest problems first.

The Simple Fixes You Can Try Right Now

1. Your Thermostat Isn't Set Correctly

The short answer: Your thermostat might be set to "off" or "cool" instead of "heat," or the temperature setting is lower than your current room temperature.

Here's what to check:

This sounds too simple to mention, but it's one of the most common service calls we get. Someone accidentally switched the thermostat to the wrong setting, or the batteries died and reset everything.

Walk over to your thermostat right now and verify:

• It's set to "HEAT" not "COOL" or "OFF"

• The temperature is set higher than the current room temperature (try setting it 5 degrees higher)

• The display is lit up (if it's blank or dim, the batteries might be dead)

• If it's programmable, check that the schedule hasn't put it in "away" mode

Try this: Replace the batteries if you have a battery-powered thermostat, then wait a few minutes to see if the furnace responds.

Why this happens: Batteries die, kids play with the buttons, or someone changes the setting without realizing it.

2. Your Furnace Power Switch Got Turned Off

The short answer: There's a light switch near your furnace (usually looks like a regular light switch, sometimes with a red plate) that might have been accidentally flipped off.

Here's what to check:

Most furnaces have a power switch mounted on or near the unit that looks exactly like a regular light switch. It's there so you can safely shut off power for maintenance, but it's also easy to accidentally flip off, especially if it's in a busy basement or utility room.

Go to your furnace and look for this switch. It might be on the unit itself, on a nearby wall, or at the top of the basement stairs. If you find it in the "off" position, flip it back on.

Try this: After turning the switch on, wait 30 seconds, then go check your thermostat. You might need to adjust it again to call for heat.

Why this happens: Someone cleaning, doing laundry, or working in the basement accidentally flips it thinking it's a light switch.

3. Your Circuit Breaker Tripped

The short answer: The circuit breaker that powers your furnace might have tripped, cutting power to the entire system.

Here's what to check:

Go to your electrical panel (breaker box) and look for a breaker labeled "furnace" or "HVAC." If the breaker is in the middle position or appears to be off, it has tripped.

Try this: Push the breaker firmly to the "off" position first, then flip it back to "on." This properly resets it. If the breaker immediately trips again, you have an electrical problem that needs professional attention - don't keep resetting it.

Why this happens: Power surges, electrical issues in the furnace, or an overloaded circuit can trip the breaker.

4. Your Furnace Filter Is Completely Clogged

The short answer: A severely clogged filter can restrict airflow so much that safety sensors shut the furnace down to prevent overheating.

Here's what to check:

When was the last time you changed your furnace filter? If you can't remember, it's probably been too long. A filter that's packed with dust, pet hair, and debris blocks airflow, and modern furnaces have safety features that prevent them from running when airflow is restricted.

Pull out your filter and hold it up to a light. If you can't see light through it, it's too clogged.

Try this: Replace the filter with a new one, wait a few minutes, then try your thermostat again. Even if this doesn't solve the problem completely, you needed a new filter anyway.

Why this happens: Life gets busy, and filter changes get forgotten. It happens to everyone.

Problems That Usually Need Professional Help

If you've checked those four simple things and your furnace still won't start, you're likely dealing with one of these issues that require a technician:

5. Your Pilot Light Is Out or Ignitor Failed

The short answer: Gas furnaces need a pilot light or electronic ignitor to start the burners. If it's out or broken, your furnace can't produce heat.

Here's what's happening:

For older furnaces with pilot lights: The small flame that should be burning constantly might have gone out. You might be able to relight it yourself if you're comfortable following the instructions on your furnace, but many homeowners prefer to have a professional handle anything involving gas.

For newer furnaces with electronic ignitors: The ignitor might have failed. You might hear clicking sounds as the furnace tries to start, but nothing happens. Electronic ignitors wear out over time and need replacement.

What you'll notice: You might hear your furnace trying to start, or you might smell a brief whiff of gas (which should stop quickly as the safety valve closes). If you smell continuous gas, leave your house immediately and call your gas company.

The fix: A technician can relight a pilot light or replace a failed ignitor, usually in under an hour. Ignitor replacement typically costs $150-300.

6. Your Flame Sensor Is Dirty or Failed

The short answer: The flame sensor detects whether the burners are actually lit. If it's dirty or faulty, it shuts the gas off for safety, preventing your furnace from staying on.

Here's what's happening:

Modern furnaces have a safety device called a flame sensor - a thin metal rod near the burners that confirms the gas is actually burning. If it doesn't detect a flame (either because it's covered in buildup or has failed), it shuts everything down to prevent gas from flowing without igniting.

What you'll notice: Your furnace might start, run for a few seconds, then shut off. This cycle might repeat multiple times.

The fix: A technician can clean or replace the flame sensor. Cleaning is usually part of a tune-up and doesn't cost extra. Replacement costs $80-250 depending on the part.

7. Your Blower Motor or Capacitor Failed

The short answer: The blower motor pushes warm air through your ducts. If it or its capacitor fails, the furnace won't distribute heat even if everything else works.

Here's what's happening:

You might hear the furnace try to start - the burners might even light - but if the blower doesn't run, the warm air stays trapped in the furnace. Safety sensors detect this and shut everything down to prevent overheating.

The capacitor is a small component that gives the blower motor the electrical boost it needs to start. Capacitors fail more often than motors and are much cheaper to replace.

What you'll notice: Silence when the furnace should be running, or you might hear humming but no air movement. Sometimes you'll smell a burning odor as the furnace overheats without airflow.

The fix: Capacitor replacement costs $150-300 and takes about 30 minutes. Motor replacement is more expensive at $400-800, but motors typically last 15-20 years.

8. Your Gas Valve or Control Board Failed

The short answer: Major control components like the gas valve or main circuit board can fail, preventing your entire furnace from operating properly.

Here's what's happening:

The gas valve controls whether gas flows to the burners. If it fails, no gas reaches the ignition system. The control board is the furnace's "brain" that coordinates all the components. When it fails, nothing works correctly.

What you'll notice: Complete system failure with no response at all, or error codes flashing on your furnace (if it has a digital display).

The fix: These are more expensive repairs - gas valves typically cost $300-600 installed, and control boards run $200-600 depending on the furnace model. At this point, if your furnace is old, it's worth discussing whether repair or replacement makes more sense.

When You Should Call for Help Immediately

You should call a professional right away if:

• You smell continuous gas (after calling your gas company first)

• You've tried the simple fixes and nothing works

• Your furnace is making loud banging, screeching, or unusual noises

• You see smoke or smell burning that doesn't go away quickly

• It's extremely cold outside and your house temperature is dropping dangerously

• You're not comfortable checking electrical panels or working around your furnace

• You have vulnerable family members (young children, elderly, or anyone with health conditions) who need heat

Remember, furnace problems that prevent startup rarely fix themselves. If simple troubleshooting doesn't work, the problem will only get worse.

What to Do While You're Waiting for Help

If you've called for service and need to wait a few hours:

Keep your family warm:

• Close off unused rooms to concentrate heat

• Use space heaters safely (never leave them unattended, keep them away from anything flammable)

• Dress in layers

• Keep bedroom doors closed at night to retain body heat

• Let faucets drip slightly if temperatures are below freezing to prevent frozen pipes

Protect your home:

• If temperatures are dropping fast and you're worried about pipes, shut off your main water valve and drain your pipes

• Set your thermostat to the "on" fan position to circulate whatever warm air remains

• Open cabinet doors under sinks on exterior walls to let warm air reach pipes

Don't do this:

• Never use your oven or stovetop to heat your home

• Don't run generators or propane heaters indoors

• Don't ignore carbon monoxide detector alarms

Start Simple, Then Get Help

Most homeowners can check the thermostat, power switch, circuit breaker, and filter themselves in about 10 minutes. If those simple checks don't solve the problem, you're dealing with something that needs professional diagnosis and repair.

The good news is that most furnace startup problems are fixable, often in a single service call. The key is not waiting too long when temperatures are dropping - the sooner you get help, the sooner you're comfortable again.

We're Here When Your Furnace Isn't

At Wischmeyer's Plumbing Plus, we've been getting Rochester furnaces running again for over 35 years. We know how stressful it is when your heat goes out, especially during our brutal winters. That's why we prioritize furnace calls and work quickly to get your heat back on.

When you call us, we'll:

• Get to you as quickly as possible (emergency service available)

• Diagnose the problem accurately the first time

• Explain exactly what's wrong and what it'll cost to fix

• Get your heat running again so you can stop worrying

We've seen every furnace problem imaginable, and we'll give you honest advice about whether repair makes sense or if it's time to consider replacement.

Is your furnace not turning on right now? Don't wait until your house is dangerously cold. Call Wischmeyer's Plumbing Plus today, and let's get your heat back on.

Quick FAQ

How long does it take to fix a furnace that won't turn on? Simple issues like replacing an ignitor or cleaning a flame sensor take 30-60 minutes. More complex repairs might take 2-3 hours. We'll give you an honest time estimate once we've diagnosed the problem.

Should I try to fix it myself? You can safely check your thermostat, power switch, circuit breaker, and filter. Anything involving gas lines, electrical components inside the furnace, or opening up the furnace itself should be left to professionals.

How much will it cost to fix? Simple repairs like ignitors or flame sensors typically cost $150-300. More significant repairs like blower motors or gas valves run $300-800. We always provide a clear estimate before starting any work.

What if my furnace is old? Should I repair or replace? If your furnace is under 10 years old, repair usually makes sense. Over 15 years old with a major repair needed? Replacement often makes more financial sense. We'll help you understand your options honestly.

Can I prevent this from happening again? Annual maintenance catches most problems before they leave you without heat. Regular filter changes, keeping the area around your furnace clear, and addressing small issues promptly all help prevent major failures.

Wischmeyer's Plumbing Plus has been keeping Rochester homes warm for over 35 years. From simple repairs to complete furnace replacement, we're here to help when your heating system needs attention.

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