Furnace won't turn on? common causes and fixes

A furnace that won't turn on in Severance is almost always caused by one of seven things: a tripped breaker or dead thermostat battery, a failed igniter or pilot, a closed gas valve, a stuck blower motor, a bad control board, a dirty flame sensor, or a safety lockout from a blocked flue. Most of these are diagnosable in under 20 minutes with a multimeter and a flashlight.

We run these calls all winter across Severance, and the pattern rarely changes. Below we walk through what to check yourself, what each failure looks like, and the point where calling a technician saves you money instead of costing you.

Start here: the four things to check before you call anyone

Before you touch the furnace, run these four checks. They cost nothing and they resolve roughly one in five no-heat calls we get in Severance.

1. Thermostat battery and mode. Pull the thermostat off the wall plate, replace the batteries (usually two AA or AAA), and confirm it is set to HEAT, not COOL or AUTO with a low setpoint.
2. Breaker and service switch. Check the breaker panel for a tripped 15- or 20-amp breaker labeled furnace or air handler. Then find the light-switch-style service switch on or near the furnace - it looks like a regular wall switch and gets flipped off by accident more often than you'd think.
3. Gas valve. The gas shutoff is a small lever on the black pipe feeding the furnace. The lever should be parallel to the pipe, not perpendicular.
4. Filter. A filter packed solid with dust will trip the high-limit switch and shut the furnace down within minutes of startup. If you can't see light through it, replace it.

If all four check out and the furnace still won't fire, the problem is inside the unit. That's where a proper diagnosis matters - guessing at parts gets expensive fast. Our team handles Furnace Repair Severance CO calls every day and can usually tell you the failed component within the first 15 minutes on site.

Why won't my furnace turn on in Severance CO?

Furnace won't turn on in Severance CO is a symptom, not a diagnosis. The unit is telling you one of its safety interlocks has opened, or a component in the ignition sequence has failed. Modern furnaces run a fixed startup sequence: thermostat calls for heat, the inducer motor spins up, the pressure switch closes, the igniter glows, the gas valve opens, the flame sensor proves flame, and the blower starts. Break any link in that chain and the furnace shuts down or never starts.

In Severance specifically, we see two patterns that don't show up as often in warmer parts of Colorado. First, the temperature swings here between a 60-degree November afternoon and a single-digit overnight low, and that cycling stresses igniters and pressure switches. Second, a lot of the housing stock in and around Severance was built in the last 15 to 20 years, which means many furnaces are now in the 12- to 18-year range - right where control boards, blower motors, and heat exchangers start failing.

If you're north of town toward the Windsor line, the same weather pattern applies. We handle Furnace Repair in Windsor with the same crew and the same diagnostic process.

Power and thermostat problems

Power and thermostat issues account for the largest share of no-start calls, and they're the cheapest to fix. A furnace needs 120 volts at the unit and 24 volts at the thermostat to do anything at all.

What to look for

• Dead thermostat display. No screen means no 24-volt control power. Usually a blown 3-amp fuse on the furnace control board, a broken thermostat wire, or dead batteries.
• Thermostat on but no call for heat. Check the schedule. A hold or away setting will override your manual bump to 72.
• Breaker trips again immediately. That's a short in the unit, not a nuisance trip. Stop resetting it.
• Furnace hums but nothing happens. You're getting line voltage but the control board isn't sending the signal - often a failed board or a bad transformer.

Thermostat replacement in this area runs $180 to $420 in 2026 depending on whether you go basic programmable or smart. If your thermostat is more than 10 years old and the display flickers, replacing it is cheaper than chasing the intermittent fault.

Ignition, pilot light, and gas supply failures

If the furnace starts its sequence - you hear the inducer fan spin for 30 to 60 seconds - but never lights, the problem is in the ignition path. This is the second-most-common failure we see.

Hot surface igniter

Most furnaces built after 1995 use a hot surface igniter instead of a standing pilot. It's a fragile silicon carbide or silicon nitride element that glows orange when it's working. If you look through the sight glass and see no glow, the igniter is either cracked or not getting voltage. Igniters are a $40 to $120 part, but the diagnostic time is what matters - you need to confirm the board is actually sending 120 volts to it before you replace anything.

Standing pilot

Older furnaces with a standing pilot can lose the flame from a draft, a dirty orifice, or a failed thermocouple. Relighting is straightforward if you follow the label on the burner door. If the pilot won't stay lit after two attempts, the thermocouple is the usual culprit - a $15 part that takes about 20 minutes to swap.

Gas supply

If you smell gas, leave the house and call 911 or the gas utility from outside. Do not troubleshoot. If you don't smell gas but the furnace won't light, check that the meter valve and the furnace shutoff are both open. In Severance, propane is common on rural lots outside the Xcel service area, and propane furnaces have their own quirks - tank level, regulator freeze-up, and orifice sizing all matter. We run Propane Furnace Repair Severance CO calls regularly for exactly this reason.

Blower motor and control board failures

The furnace lights, runs for a few minutes, then shuts off before the house warms up. That's a blower or control board problem, and it's the failure mode that fools the most homeowners because the furnace clearly "works" for a little while.

Three things cause it:

• Failed blower motor. The motor won't spin, heat builds up in the plenum, and the high-limit switch trips. You'll hear the burners light and then shut off 90 seconds later, over and over.
• Bad capacitor. The motor hums but doesn't turn. A $25 capacitor fixes it - if you catch it before the motor burns out from the strain.
• Control board failure. Cracked solder joints, burnt relays, or a failed ignition module. Boards run $250 to $650 installed in 2026, and availability depends on the brand.

We see a lot of Carrier and Trane equipment in Severance homes, and both brands have known board and blower failure points at the 10- to 15-year mark. If you're not sure what you have, the model and serial plate inside the upper door tells you everything. Our Furnace Blower Motor Repair Severance CO work covers diagnosis, capacitor replacement, and full motor swaps on most residential brands.

How do I fix a furnace that won't start in Severance?

You fix a furnace that won't start in Severance by working the startup sequence in order: confirm power at the unit, confirm the thermostat is calling for heat, confirm the inducer runs, confirm the igniter glows, confirm the flame proves, confirm the blower starts. The first step that fails is your problem.

Here's the practical version:

1. Reset the furnace once. Turn the thermostat off, kill power at the service switch for 30 seconds, restore power, and call for heat. A one-time lockout from a power blip will clear. A real fault won't.
2. Read the LED code. Most furnaces have a blinking LED on the control board behind the lower door. Count the flashes and look up the code on the wiring diagram taped inside the door. This single step saves more time than anything else you can do.
3. Check the flame sensor. A dirty flame sensor is the number-one cause of "lights then shuts off in 5 seconds." It's a thin metal rod in front of the burner. Cleaning it with fine steel wool fixes it about 70 percent of the time.
4. Check the flue and intake. Snow, ice, or a bird nest in the PVC intake or exhaust will trip the pressure switch and lock the furnace out. In January, this is common on high-efficiency units with sidewall venting.

If you get past step four and the furnace still won't run, stop. You're into component-level diagnosis that needs a meter and a wiring diagram.

Common mistakes that make it worse

The mistakes we see most often on no-heat calls in Severance are the ones that turn a $200 repair into an $1,800 one.

• Resetting the breaker repeatedly. If it trips twice, there's a short. Every reset pushes current through damaged wiring.
• Replacing parts by guess. Throwing an igniter, then a board, then a sensor at a furnace gets expensive. Diagnose first, replace once.
• Running the furnace with a blocked filter. A restricted filter overheats the heat exchanger. Cracks follow, and a cracked heat exchanger means a new furnace, not a repair.
• Ignoring the smell of gas. If you smell rotten eggs near the furnace, get out and call the utility. No exceptions.
• Blocking the return air. Furniture or boxes over the return grille starve the blower and cause the same overheating cycle.
• Skipping annual service. A $99 to $149 tune-up each fall catches igniter wear, dirty sensors, and failing capacitors before they strand you at 10 p.m. in January.

If your system is past 15 years and you're facing a heat exchanger or control board replacement, run the numbers before you commit. Sometimes repair is right. Sometimes it isn't. Our Furnace Repair Cost Severance CO guide breaks down what each common repair actually costs in this market so you can compare against replacement.

When to call a professional

Call a professional when the furnace won't fire after a single reset, when you smell gas, when the breaker trips twice, when you see a cracked or sooty heat exchanger, or when the furnace is more than 15 years old and the repair quote tops $800.

Those are the calls where DIY troubleshooting stops being safe or cost-effective. Gas valves, control boards, heat exchangers, and venting all fall under code requirements that a homeowner can't verify without the right tools - and a botched repair on a gas appliance is a carbon monoxide risk, not just a comfort problem.

Severance Furnace Repair Pros handles no-heat calls across Severance and the surrounding Weld County communities. We diagnose first, quote the repair before we start, and carry common parts on the truck so most calls are finished in one visit. If you're in a neighboring town, we cover Furnace Repair in Johnstown and the rest of the corridor along Highway 392 with the same response times.

Frequently Asked Questions

Why won't my furnace turn on in Severance CO?

The most common causes are a tripped breaker, dead thermostat batteries, a closed gas valve, a clogged filter, a failed igniter, or a dirty flame sensor. In Severance, cold snaps and older 12- to 18-year-old furnaces make igniter and control board failures especially common between November and March.

How do I fix a furnace that won't start in Severance?

Reset the furnace once at the service switch, check the thermostat batteries and mode, confirm the gas valve is open, replace the filter, then read the LED blink code on the control board. If it still won't fire after that, the fault is inside the unit and needs a technician with a multimeter.

Should I call a pro if my furnace won't turn on in Severance?

Yes, if it won't fire after one reset, if the breaker trips twice, if you smell gas, or if the furnace is over 15 years old. Those situations involve gas valves, control boards, or heat exchangers - components where a wrong diagnosis risks carbon monoxide or a much larger repair bill.

What causes a furnace to not turn on in Severance Colorado?

Seven things cover nearly every case: no power at the unit, thermostat failure, ignition failure, gas supply interruption, blower motor failure, control board failure, or a safety lockout from a blocked flue or dirty flame sensor. The LED code on the board tells you which one.

How much does furnace repair cost in Severance in 2026?

Typical 2026 repairs here run $180 to $420 for a thermostat, $200 to $500 for an igniter or flame sensor, $250 to $650 for a control board, and $400 to $900 for a blower motor. Diagnostic fees usually run $79 to $129 and are often credited toward the repair.

Get help with Furnace Repair in Severance

If your furnace won't turn on and you've run the basic checks, we can be at your door today. Call Severance Furnace Repair Pros at (970) 1234567 and we'll diagnose the fault, quote the repair before we start, and get your heat back on.