Furnace Won't Ignite: 7 Most Common Utah Causes
Furnace blower running but burner won't light? Here's the diagnostic order Utah HVAC techs use and what's safe for a homeowner to check first.
Furnace not igniting almost always means: no spark, no gas, or a safety lockout. Modern furnaces are smart — they try ignition 2–3 times then lock out for 60 minutes. Watching one full cycle through the inspection window tells you 80% of what you need to know.
Diagnostic
Most likely causes (in order)
Walk through the list top-to-bottom. The first cause matches roughly half of cases we see in Utah; if it doesn't fit your symptoms, move to the next.
Failed igniter (silicon carbide hot surface)
The igniter is a thin gray rod that glows orange just before gas opens. Average life: 6–10 years. When it cracks (vibration + thermal cycling), the furnace tries 2–3 times then locks out.
Dirty flame sensor
Flame lights, but the sensor doesn't detect it (mineral coating). Gas valve closes within 5 seconds. Looks identical to ignition failure but is a different fix.
Gas supply issue
Closed gas valve at the meter, partially closed shutoff valve at the furnace, or the gas company shut off service during a recent leak repair next door.
Clogged condensate drain (96%+ AFUE only)
High-efficiency furnaces have a condensate trap that fills with water during operation. If the drain line clogs, the float switch opens and locks out ignition. Common in Utah hard water — scale builds up in the trap.
Pressure switch / vent obstruction
Furnace exhaust vent (sidewall PVC or roof vent) blocked by snow, ice, animal nest, or installation debris. Pressure switch can't sense draft, locks out ignition.
Failed control board
The control board sequences ignition. Failure = no cohesive cycle. Check for any LED diagnostic blink codes through the inspection window.
Bad thermostat / wiring
Thermostat not calling for heat, or call signal not reaching the control board. Less common but worth ruling out.
DIY first
Safe checks you can do today
Each step is labeled by safety level. Stop at any “Pro only” step — that's where the diagnostic crosses into work that needs gauges, multimeters, or live electrical access.
Check thermostat is set to HEAT and 5°F+ above room temp
Safe DIYQuick. Confirms a heat call is being made.
Confirm gas at the furnace shutoff valve
Safe DIYBlack valve on the gas line at the furnace. Should be parallel to the pipe (open). Other gas appliances (range, water heater) work? Confirms gas to the building.
Reset the furnace switch (the wall switch next to it)
Safe DIYToggle off, wait 30 seconds, toggle on. Lets the control board clear any 60-minute lockout. Watch through the inspection window for a fresh ignition cycle.
Check the LED blink code on the control board
Safe DIYManufacturer-specific (look at the inside of the panel door for the legend). Tells you exactly which fault tripped. Snap a photo to text us.
Stop here if no cycle starts
Pro onlyBeyond this is gauges, multimeter, and replacement parts. Call us — diagnostic is $89 and credited toward repair.
Stop and call
When you should call us instead
- Furnace makes a clicking or buzzing sound but doesn't ignite
- You smell gas (any amount) — leave the home and call the gas company first, then us
- Snow or ice has covered the sidewall vent or roof vent — clear it first, then if still no ignite, call
- Furnace is 12+ years old AND won't ignite — repair vs. replace decision
Not sure if it's a real problem?
Our AI walks you through the same triage a senior tech would — figures out whether you need a service call or whether it's something simpler you can handle yourself. Or skip ahead and book a diagnostic visit.
FAQ
Frequently asked questions
How much does an igniter cost to replace?
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Igniter part: $35–$95. Labor: 30 minutes. Most Utah no-heat calls land at $185–$260 for igniter replacement including diagnostic. Same-day service in heating season.
Why does it ignite sometimes but not always?
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Intermittent ignition is usually a flame sensor (working only when clean) or a marginal igniter (working when warm but cracking when cold). Both are cheap fixes once diagnosed.
Related
More diagnostic guides
Other common Utah-home symptoms with the same step-by-step diagnostic format.
