When a Denver cold snap settles in after sundown and the house goes quiet, that’s when a fussy furnace makes itself known. You hear the thermostat click, maybe the inducer fan starts, then nothing. Or the burner lights with a whoosh, only to go dark a second later. Those moments often trace back to the same culprits: pilot light or ignition problems. After years of crawling through crawlspaces in Arvada, pulling burners in Park Hill, and answering no-heat calls from Highlands Ranch to Thornton, I can tell you these issues are common, fixable, and easier to prevent than most people think.
This guide walks through how ignition systems work, why Denver’s climate magnifies certain failures, how to triage the problem safely, and when to lean on a pro for gas furnace repair Denver homeowners can trust. I’ll also cover how routine furnace maintenance Denver residents schedule in the fall can head off most winter breakdowns, plus the point at which furnace replacement Denver becomes the smarter move.
Why ignition problems spike in Denver winters
Denver packs a few variables into a furnace’s daily life. High altitude, dry winter air, and big temperature swings combine in ways that stress combustion and ignition parts.
Altitude reduces oxygen density. Combustion needs the right mix of fuel and air, and thinner air changes the ratio. Many furnaces in the metro area are set up or orificed for elevation, but a slightly dirty burner, a borderline flame sensor, or a weak spark can slip from marginal to failing on a bitter night. Dry air accelerates dust buildup. Every time your blower kicks on, it moves fine particulates that settle in the burner compartment, on flame rods, and in the pilot assembly. Dust isn’t just cosmetic; it insulates sensors from the flame and disrupts the spark path.
Wind matters too. In neighborhoods like Green Valley Ranch or Stapleton, straight west winds can backdraft through poorly terminated vents or through rooftop caps that lost their bird screens. A gust can snuff a pilot the same way you’d blow out a candle.
Ice and snow create their own havoc. A high-efficiency furnace with a sidewall PVC intake can pull in powder during a storm. A little rime around the pipe mouth narrows the intake, the pressure switch fails to close, and the ignition sequence stops before the burners even try to light. If your furnace behaves on calm days and balks during storms, start by taking a careful look at the venting outside.
Standing pilot vs modern igniters
Older furnaces use a standing pilot, a small flame that burns constantly and lights the main burners when the gas valve opens. Newer units use electronic ignition: either a hot surface igniter that glows orange and lights the gas, or a spark igniter that throws a spark at the burner. Each style fails differently.
Standing pilots go out when the thermocouple can’t prove flame, the pilot tube is partially clogged, or drafts hit the pilot flame. Thermocouples are inexpensive, pencil-thin sensors that sit in the pilot flame and generate a tiny voltage. I’ve replaced more of these than I can count in central Denver bungalows and Lakewood ranches. They don’t last forever, especially if the pilot flame has been burning a little yellow or lazy. A thermocouple that reads borderline will hold the pilot for minutes on a warm day, then trip after seconds when the air turns colder and the flame shrinks.
Hot surface igniters look like gray ceramic sticks. They glow like a toaster element. They crack easily if touched, and their resistance changes as they age. Many go five to seven heating seasons. A small hairline crack is enough to keep them from reaching ignition temperature, and they often fail silently. If you hear the inducer run and the igniter doesn’t glow, check the viewport. No glow usually means the igniter is done. Spark igniters fail less often, but they can carbon up at the tip, or a poor ground can weaken the spark.
How the ignition sequence is supposed to run
Understanding the rhythm helps you pinpoint the break in the chain. On a call for heat, the thermostat signals the control board. The inducer fan starts to clear the heat exchanger and establish draft. The pressure switch verifies the vent is clear. Once the board is satisfied, it energizes the igniter. After a prepurge delay, the gas valve opens and the burners light. A flame sensor sees steady flame and tells the board, which keeps the gas flowing. Finally, after a short delay, the blower starts to push warm air through your ducts.
If something breaks, the control board usually tries again a few times, then locks out. Many boards show a flashing code behind a small window. Count the flashes. Two flashes versus three can tell a tech whether the pressure switch failed or the flame wasn’t proven. Write that number down before you hit the power switch.
Safety first
If you smell gas, do not troubleshoot. Leave the house, call your utility or a qualified pro from outside. If you only have intermittent heat and no gas smell, turn off power to the furnace at the switch or breaker before opening the cabinet. Let the furnace sit for a few minutes to clear any residual gas. If you aren’t comfortable working around gas components, don’t. The best furnace service Denver offers starts with safe practices.
Simple things homeowners can check
Over the years, I’ve talked a lot of people through quick fixes that save a service call, especially on a Sunday night. None of these requires tools, and all stay on the safe side of the line between homeowner and technician.
- Confirm the thermostat is calling for heat, set to heat mode, and has fresh batteries if it uses them. Try raising the setpoint five degrees. Check the furnace switch, often at the top of the basement stairs, and the breaker in the panel. A tripped breaker can be reset once. If it trips again, stop and call. Look at the furnace’s intake and exhaust outside. Clear snow, leaves, and nests gently. Don’t stick tools into the pipes. Replace a dirty furnace filter. A severely clogged filter can disrupt airflow and cause short cycling that looks like an ignition problem. Observe the furnace through the sight glass. Note whether the igniter glows, whether the burners light briefly then go out, and whether any diagnostic LED is flashing. Record the pattern.
That last point helps when you call for gas furnace repair Denver technicians can respond faster when you can say, for example, “it lights for three seconds, then shuts down, and the board flashes one long, two short.”
When the pilot light won’t stay lit
If you have an older furnace with a standing pilot and it won’t hold flame, suspect the thermocouple first. The flame should be steady, mostly blue, and envelop the top third of the thermocouple. If it’s small or yellow-tipped, the pilot orifice may be restricted. Spiders and dust love pilot assemblies. I’ve pulled out orifices in Wheat Ridge homes that looked like they were stuffed with lint, and once the pinhole was clear, the flame perked up and the thermocouple started generating enough millivolts to keep the gas valve open.
Drafts are another culprit. A fan in the same room, a loose furnace door, or a gap in the flue can flicker the pilot. In Denver’s older homes with draft-hood furnaces, the metal vent connector sometimes loses pitch over time. A small sag can cause intermittent backdrafting, which shows up as a sooty pilot and burn marks around the draft hood. That’s a professional repair.
One more trap: modern water heaters with power vents or large kitchen range hoods create negative pressure. On a cold morning, that negative pressure can pull air down the furnace flue and snuff the pilot. If the pilot seems fine until the big hood fan kicks on, you’ve found the interaction. A pro can look at makeup air and vent sizing.
Electronic ignition problems, symptom by symptom
If the igniter doesn’t glow at all, check whether the inducer runs. No inducer suggests a power or control issue. If the inducer runs and the igniter never glows, the igniter or the control board may be at fault. Hot surface igniters are fragile. I’ve seen brand-new ones crack from an accidental tap during installation. If yours glows but doesn’t light the burners, the gas valve may not be opening, or there’s no gas flow at the manifold. An experienced tech will check manifold pressure and confirm the valve is getting 24 volts.
Burners that light, then drop out within a second or two point to the flame sensor. This small metal rod sits opposite the igniter and detects flame through microamps of current. If it’s coated with oxide, it can’t read the flame, so the board kills gas as a safety. A gentle cleaning with a non-abrasive pad often buys you another season, though a heavily pitted rod should be replaced. I’ve had plenty of calls in Capitol Hill where a five-minute cleaning got the heat back on for the night.
Spark ignition adds two wrinkles. The spark electrode gap must be correct, and the ground must be solid. A corroded grounding screw or a wire that looks fine but is loose can weaken the spark. If you hear ticking but the burner doesn’t light, check for gas flow and flame rollout issues. If the burner lights but the spark keeps clicking, the flame sense path may be poor, and the board “thinks” there’s no flame.
Altitude and combustion tuning
At 5,280 feet and above, gas appliances use different orifices and sometimes different pressure settings. Newer furnaces are often shipped with conversion kits or factory-adjusted models labeled for high altitude. If a furnace was installed without proper altitude setup, it may run rich or lean. Rich combustion leaves soot, which coats flame sensors and clogs burner ports. Lean combustion struggles to ignite and can pop on light-off. When we perform furnace service Denver wide, part of a proper tune-up is checking manifold pressure with a manometer and comparing flame characteristics to the equipment’s specs.
Even with the right parts, winter barometric swings can expose a borderline setup. If your furnace seems to behave perfectly on mild days and struggle on arctic ones, a tech can check the venting and the gas supply under load. Utilities in the metro area maintain good pressure, but long, undersized runs inside the house can drop pressure when multiple appliances fire at once.
Prevention through thoughtful maintenance
Most ignition and pilot problems have early warning signs. A fall furnace tune up Denver homeowners schedule in September or October pays for itself by catching these. A good service visit isn’t a quick vacuum and a filter swap. It’s a methodical cleaning and test cycle.
I run a brush through each burner port to knock out rust scale, clean the flame sensor with a fine pad, and check igniter resistance. Hot surface igniters have a resistance range that tells you if they’re approaching end of life. If an igniter is reading high, I’ll recommend replacing it proactively rather than waiting for a 2 a.m. failure on a ten-below night. I also verify the thermostat anticipator setting on older models, inspect the heat exchanger for cracks with a mirror and light, and confirm the pressure switch holds steady during a full cycle.
For high-efficiency units, I inspect and flush the condensate trap. A partially clogged trap can trip safety switches and shut down ignition, especially when the furnace cycles frequently. I also check the intake and exhaust terminations outside and make sure clearances are maintained around shrubbery and snow lines.
If you’ve skipped a few years of maintenance, a thorough furnace maintenance Denver visit can still pull a lot of reliability back into the system. It’s not unusual to turn a finicky igniter and temperamental flame sensor into a solid heating season with ninety minutes of careful work.
Common parts, typical costs, and what’s worth fixing
Homeowners ask for ballpark numbers, and while every job is different, patterns emerge.
Thermocouples for standing-pilot furnaces are inexpensive parts, and total repair cost is usually modest. Hot surface igniters cost more than thermocouples but are still middle-of-the-road repairs. If a control board is failing to power the igniter or misreading flame current, that’s a bigger ticket, but still often worthwhile on a mid-life furnace. Gas valves sit in the same category: not cheap, worth replacing on a sound unit, questionable on a 20-year-old one with rusted burners and a thin heat exchanger.
If a tech starts listing multiple ignition and safety components in one visit - igniter, flame sensor, control board, pressure switch - pause and consider age and condition. That’s often the moment to discuss furnace replacement Denver options. Repairing three or four core components on a system that’s past 15 years can be false economy, especially if the heat exchanger shows early signs of failure. A new unit with proper Furnace Installation Denver CO setup, altitude adjustments, and warranty support may be the better path.
DIY boundaries vs professional service
Cleaning a flame sensor, changing a filter, and clearing a vent termination are within reach for many homeowners. Adjusting gas pressure, disassembling burners, or replacing ignition control boards crosses into licensed work that carries safety risks.
When choosing a provider for gas furnace repair Denver residents should look for a few markers. Ask whether the techs carry manometers and combustion analyzers, not just multimeters. Ask if they adjust for altitude and verify manifold pressure under load. A proper diagnostic includes watching a full heat cycle, not just swapping the obvious failed part. If they offer furnace service Denver seasonal specials, ask for a checklist, not just a price.
On the install side, Furnace Installation Denver CO should include a venting assessment, duct static pressure readings, and commissioning data like temperature rise and combustion analysis. Too many installs skip these and leave you with a furnace that technically runs but lights poorly, cycles short, and eats igniters every other year.
Stories from the field
Two winters ago in Five Points, I met a family with a nine-year-old high-efficiency furnace that quit during a snowstorm. The inducer ran, the igniter glowed, but no flame. Outside, the intake showed a delicate lace https://gregorytffx850.almoheet-travel.com/furnace-replacement-denver-co-avoiding-hidden-costs of ice that barely looked like blockage. We cleared the ice, warmed the first few inches of pipe with a hair dryer, and the furnace lit immediately. We later added a simple hooded intake termination with better wind protection. One small change, no further no-heat calls that season.
In Littleton, a 1990s standing-pilot furnace would light and hold for twenty seconds, then drop. The pilot looked healthy. The owner had replaced the thermocouple twice. The real problem was a tired combination gas valve that sagged after it warmed. It passed a cold start but lost coil strength during operation. A manometer and a little patience found it. We replaced the valve and cleaned the pilot assembly. The difference between guessing and diagnosing is tools and time.
Edge cases worth noting
Some furnaces light only on the second or third try. The owner hears click, pause, click, then it finally roars to life. That intermittent pattern often points to dirty burners and poor cross-lighting. Gas reaches the first burner, lights, but the flame doesn’t carry quickly across to the others. The control board doesn’t see full flame in time and shuts down, then retries. A good cleaning of the crossover ports usually cures it.
Another oddball: furnaces installed in tight mechanical rooms after a remodel. The unit originally had a louvered door and plenty of makeup air. A remodeler swapped the door for a solid slab, and now the furnace struggles to maintain flame. If the room starves for air, you can get weak ignition and sooty operation. The fix is simple - restore makeup air - but it takes a tech who looks at the room, not just the furnace.
Smart thermostats can also complicate ignition timing. Some need a common wire and will pull power in ways that confuse older control boards. If issues started right after a thermostat upgrade, try a basic digital thermostat for a day. I’ve seen intermittent lockouts disappear when a power-stealing thermostat was replaced or a proper C-wire was added.
What a thorough tune-up includes
When I describe a complete furnace tune up Denver customers can expect, it includes cleaning, inspection, and numbers. Numbers are key. Temperature rise across the heat exchanger should match the manufacturer’s range. Too low suggests excessive airflow or undersized gas input; too high suggests restricted airflow. Manifold pressure should be at spec, often around 3.5 inches water column for natural gas at sea level, adjusted for altitude and manufacturer’s guidance. Igniter resistance is measured and logged. Flame sensor microamps are checked. Blower capacitor readings are noted, because a weak capacitor can slow the blower and push temperature rise out of range, which then leads to limit trips and ignition cycles that look like burner problems.
Venting is inspected top to bottom, with slope checked on metal vent connectors and joints resealed if needed. On condensing furnaces, the condensate trap is cleaned and the drain run checked for proper slope and freeze risk. Filters are replaced, and owners get a schedule that matches their usage and home conditions. A family with a couple of big dogs in Wash Park might swap filters every month in winter, while a condo couple with no pets can stretch a filter to 90 days.
Deciding between repair and replacement
No one wants to talk about replacement on the coldest day of the year, but sometimes it’s the honest answer. If your furnace is past 15 years, needs a gas valve and control board, shows rust flakes in the burners, and has a rising trend of repairs, it’s time to weigh Furnace Replacement Denver CO options. Newer high-efficiency units offer better modulation, quieter operation, and tighter safety controls. More importantly, they come with clean slates: new heat exchangers, fresh burners, new igniters, and calibrated controls.
Still, repair has its place. If a twelve-year-old furnace needs a flame sensor and an igniter, repair it and plan for eventual replacement. If your unit is under warranty, even better. Keep your receipts, register parts, and have a record of furnace maintenance Denver providers performed. Manufacturers honor clean records.
When you do replace, insist on commissioning data at the end of the install: manifold pressure, temperature rise, static pressure, and combustion analysis numbers. Those few lines on a work order prevent a lot of ignition trouble in the first five years.
How to keep heat steady through a Denver winter
Think in layers. Schedule professional maintenance before Halloween. Change filters on a schedule that matches your home. Check outdoor vents after storms. Listen to your furnace. New noises or longer start cycles are early warnings.
If you hit a no-heat situation, note the symptoms carefully. Describe what you hear and see: inducer on, igniter glow or not, burners light then die, any flashing codes. That information trims time off a service call. When you call for gas furnace repair Denver companies can often prioritize you during a cold snap if you can report a likely flame-sensing issue versus a full shutdown.
Above all, treat ignition as the heartbeat of your furnace. It’s a small part with outsized influence. Keep it clean, tuned, and properly grounded, and it will carry you through those ten-degree mornings when the sky is brightest blue and the air feels like glass.
Tipping Hat Plumbing, Heating and Electric
Address: 1395 S Platte River Dr, Denver, CO 80223
Phone: (303) 222-4289