San Diego doesn’t get the Midwest’s ice storms, but a damp 50-degree night off the ocean cuts right through a house. If your furnace won’t light, you feel it fast. Most of the no-heat calls I see around coastal and inland neighborhoods trace back to ignition trouble. The parts and patterns vary by brand and age, but the logic of how ignition works is consistent. Understand that, and you can decide what to check first, when to call a licensed hvac company, and how to avoid the same failure later.
What “ignition” means in a modern gas furnace
Ignition is the controlled process that lights the gas-air mix in the burner compartment. Older furnaces used standing pilot flames. Most San Diego homes now run on hot-surface igniters or intermittent spark systems combined with electronic control boards. The sequence is predictable: the thermostat calls for heat, the draft inducer starts, the pressure switch proves airflow, the control board powers the igniter, gas valve opens, flame sensor confirms flame, and the blower pushes warm air through the ducts. If any one step fails, the furnace either retries or locks out.
That chain reaction saves you from dangerous gas buildup. It also means a failure can look like the furnace trying to start, then quitting. Homeowners often describe it as “clicks, hums, then nothing,” or “starts, heats for a minute, shuts down.” Those details matter when troubleshooting.
The usual suspects when furnaces won’t light
After a few decades working as an hvac contractor in coastal California, you start to recognize patterns tied to our environment. Salt air, dust from dry seasons, and occasional power blips leave a signature.
Hot-surface igniters crack from age or contamination. These parts glow orange-hot, then fade again in cycles numbering in the tens of thousands. They’re brittle and can fail just from being touched with oily fingers. I’ve replaced countless igniters that looked fine but measured open-circuit with a meter.
Flame sensors get dirty. The flame rod sits in the burner flame and sends a tiny microamp signal back to the board. Any oxidation or soot interrupts the signal and the board thinks the flame went out. The furnace shuts gas and tries again, sometimes three to five times before lockout. A gentle cleaning often restores perfect operation.
Pressure switches trip because the inducer can’t pull enough air. Around San Diego, wet coastal grime or spider nests in the vent pipe are common. A clogged condensate trap on high-efficiency units will do the same thing. I’ve seen pressure switch hoses fill with water after a big storm. You can hear the inducer run, but the switch never closes, so no ignition.
Gas supply issues surface during the first cold snap when more neighbors fire up their heaters. Low gas pressure, partially closed gas cocks, or a failing gas valve lead to erratic ignition. I’ve measured manifold pressure dropping under load and watched a flame roll back then extinguish.
Control boards fail after years of thermal cycles, but I replace boards far less often than igniters or sensors. Boards can show burnt traces, swollen capacitors, or relay chatter. Before condemning a board, I confirm the inputs and outputs with a meter and manometer. It’s too easy to blame the computer when the real issue is airflow or a dirty sensor.
Safety first, even if the fix looks simple
There is a clear line between homeowner-friendly checks and tasks for trusted hvac contractors. You can reset power, replace filters, and verify the thermostat settings. You should not disassemble gas valves or bypass safety switches. Carbon monoxide doesn’t care about good intentions. If there’s any sign of soot, melted wiring, or a burnt smell, shut it down and call a licensed hvac company.
Quick checks that can save you a service call
If your furnace fails to ignite, a few simple steps can reveal whether you have a small nuisance or a deeper problem. Only attempt these with the power switch off and with the confidence you won’t forget a panel or leave a wire loose. If you smell gas at any point, stop and contact your gas utility and an hvac repair service San Diego residents rely on.
- Confirm thermostat mode and setpoint. Heat mode selected, set a few degrees above room temperature. If it’s a smart thermostat, ensure it actually has heat enabled and that the batteries (if any) are fresh. Replace or remove a severely clogged filter. Restricted airflow can trigger limit switches and confuse the ignition sequence. If you pull a filter and hear the furnace start, you found your culprit. Run only temporarily without a filter. Check the furnace power switch and breaker. Many furnaces have a switch that looks like a light switch. It gets flipped off during attic work or by accident. Make sure the front door panels are seated. Most units have a door safety switch that disables operation when the panel is off or cocked. Look at the exhaust and intake terminations outside. Birds, leaves, or salt-crusted screens can block airflow. Clear anything obvious without forcing parts out of place.
If the furnace still won’t light, note the behavior. Count flashes on the diagnostic LED on the control board. That code is gold when you talk to an hvac company near me or schedule hvac repair San Diego technicians can perform same day.
How pros diagnose ignition step by step
Arriving at a home in North Park one December, I met a three-year-old high-efficiency unit that would run the inducer for 20 seconds, then stop. The board flashed a two-blink pressure code. The homeowner had replaced the filter and checked the vent wall cap. Our next moves illustrate a typical diagnostic flow.
I start by measuring inducer vacuum at the pressure switch port with a manometer. If it barely moves, I check the exhaust and intake all the way back to the unit, including the condensate trap. On high-efficiency models, a plugged trap or sagging drain line leaves water in the secondary heat exchanger, which starves airflow. In that case, I found milky water in the trap from PVC glue residue. A flush, re-pitching the line, and the unit lit instantly.
If pressure looks strong and the switch still won’t close, I test the switch with a meter while inducing gentle vacuum. A switch that only closes at a higher-than-rated pressure needs replacement. But I only replace after ensuring the venting is clear and the inducer amperage sits in spec.
For hot-surface igniters, resistance tells the story. Most silicon nitride igniters read in the tens of ohms. Infinite resistance means a cracked element. I prefer handling the part with gloves and I always kill power to prevent accidental shorting during removal.
Flame sensors get polished gently with a fine abrasive pad, then wiped clean. I test flame signal current with a microamp meter in series. Healthy signals usually fall between 2 and 6 microamps depending on the system. Anything under about 1 microamp leads to nuisance dropouts.
When I suspect a gas valve or low supply pressure, I measure inlet and manifold pressure with a manometer while the furnace runs. Natural gas often targets around 7 inches water column at inlet and 3.2 to 3.5 inches at manifold for many residential furnaces, though you always follow the data tag. If pressure sags when other appliances fire, you likely have a supply issue that needs the utility or a line upgrade, not just a new valve.
Why San Diego’s climate creates specific ignition challenges
Salt air doesn’t just rust grills, it films components inside attic and garage furnaces. Igniters and flame sensors become less tolerant of that residue. I’ve opened units two miles from the coast and found a gray sheen on nearly every bare metal part. Regular cleaning and slightly shorter service intervals help.
We also ride through mild winters where furnaces sit idle for months, then run hard during a week of damp nights. Long idle periods allow spiders to web up vent piping, and condensate traps dry out and leave mineral crystals that later clog. If your unit lives in an attic, summer heat can age electronics faster. I see control boards from attic installs fail two to five years earlier than the same model in a garage.
Power reliability matters too. Short blips during wind events or utility transitions can scramble control boards or leave the furnace mid-cycle. A simple surge protector rated for HVAC loads can add a layer of protection. It’s not a cure-all, but it’s better than nothing, especially for homes in older neighborhoods with shared transformers.
When replacement parts are the smart move
A functioning ignition system is not a single part, it is a coordinated set of components. Replacing a cracked igniter is straightforward and cost-effective. Swapping a flame sensor takes minutes. Replacing a control board deserves more scrutiny.
If your furnace is under 10 years old and well maintained, a new board makes sense if it tests bad and the rest of the system is solid. If your unit is 15 to 20 years old and you’re stacking repairs, you should weigh the cost of a new board, inducer, and recurring service against a modern furnace with higher efficiency and warranty coverage. San Diego energy costs and mild winters mean the payback for ultra-high AFUE models isn’t always dramatic, but comfort and reliability improve once the core components are fresh.
A trusted hvac contractor can walk you through honest numbers. One spring, a homeowner in Clairemont had two board failures in 18 months on a 16-year-old furnace that sat in a hot attic. We could have ordered a third board, but the blower bearings were starting to sing and the heat exchanger had rust spots. They chose a mid-range furnace that cut noise and improved airflow, and they haven’t called for heat issues since.
The case of intermittent ignition: chasing ghost problems
The toughest calls feature a furnace that works perfectly when you arrive. Intermittent ignition failures often point to borderline conditions. A flame sensor might be just clean enough in the morning and too oxidized at night. Manifold pressure might sit at the minimum allowable and drop when the water heater fires. A pressure switch might barely close on a cold moist night when the vent has more resistance.
On a hillside property in La Jolla, a condensing furnace would fail only after sea fog rolled in. Moisture added just enough drag in the long horizontal vent run to flirt with the pressure switch setpoint. We shortened the horizontal run, added proper support to eliminate low spots, and cleaned the trap. The problem disappeared. The lesson is that system design and venting layout matter as much as the mechanical parts.
What service from a licensed hvac company actually includes
People sometimes picture “clean and check” as a quick vacuum and filter swap. Proper maintenance and diagnostic work is more thorough. If you bring in an hvac repair service San Diego homeowners recommend, ask what they do for ignition reliability. The essentials should include:
- Inspect, test, and if needed replace the hot-surface igniter. Verify resistance and proper voltage delivery from the board. Clean the flame sensor and confirm flame signal microamps under operating conditions. Test pressure switch function with a manometer and meter. Inspect venting, inducer wheel, and condensate drains for blockages or standing water. Measure gas inlet and manifold pressure during ignition and steady burn. Compare to the data plate and adjust within manufacturer limits when allowed. Verify temperature rise, blower speed settings, and limit switch operation. Excess temperature rise stresses components and shortens igniter life.
That level of work prevents most no-heat calls when the first cold nights arrive. It also builds a baseline. Once you know the signal readings when the system is healthy, you can spot drift months later.
How to choose the right team for the job
San Diego has plenty of hvac contractors. The right fit combines technical skill, communication, and follow-through. Licensing and insurance are non-negotiable. Ask for proof. A licensed hvac company San Diego residents trust will happily provide their CSLB license number, evidence of liability coverage, and worker’s comp for their technicians. Ask how they train on ignition systems for different brands. Ask how they handle parts availability and warranty claims.
Local presence matters. A san diego hvac company that stocks common igniters, flame sensors, and pressure switches can restore heat in one visit. If you’re searching “hvac company near me” during a cold snap, prioritize those who can describe their diagnostic process and provide a clear quote, not just a trip charge with vague promises.
Look for technicians who take measurements and explain them in plain language. If someone condemns a control board without showing voltages, pressure readings, or signal codes, you’re bearing too much risk. Ignition faults are measurable.
Common myths that complicate ignition troubleshooting
I hear a few repeated assumptions that send homeowners in circles. One is that you can judge a flame sensor by sight alone. A shiny sensor can still read weak. The microamp test decides.
Another is that more glow means a healthier igniter. A dying igniter can glow bright but fail mechanically or have too much resistance. The meter wins again.
Then there’s the belief that bypassing a pressure switch or jumpering a safety “just to test” is harmless. It is not. You can allow gas to flow without a verified draft, and that’s an avoidable hazard. A licensed hvac company uses manometers and test procedures that preserve safety circuits.
Finally, people sometimes think upgrading the thermostat will fix ignition. Thermostats can cause short cycling or no-call-for-heat issues, but once the furnace has started its sequence, ignition depends on the furnace itself, not the wall control.
The economics of repair versus replacement for ignition issues
A typical hot-surface igniter replacement, including diagnosis, runs less than replacing major blower components or heat exchangers. Flame sensor cleaning is usually minor. Pressure switch replacements sit in the middle, especially if coupled with clearing condensate lines. Control boards and gas valves are the big-ticket ignition-related parts, and costs vary by brand and availability.
When I advise homeowners, I map costs against age and condition. If your furnace is under 12 years old, has a clean heat exchanger and solid blower, repair is usually the smart move. Between 12 and 18 years, I look at the trend. If you’ve had three significant calls https://maps.app.goo.gl/1cASZViFR7WFXzuD9 in two seasons, you may be chasing reliability. Over 18 years, even if a repair will get you heat tonight, we talk about the risk of a follow-up failure on an unrelated component. There isn’t a single right answer, but there is a right answer for your house and timeline.
Preventive habits that make ignition problems rare
You can’t stop wear and tear, but you can extend the life of your ignition system. Change filters on schedule. Keep the condensate drain clear and pitched. Give the furnace room to breathe, with three feet of clear space around the unit if possible. Avoid storing paint thinner or corrosive chemicals near the furnace, especially in garages where vapor can corrode components.
Schedule annual service in late summer or early fall, before the first cool nights. A short appointment to clean the flame sensor, verify gas pressures, and test the pressure switch can prevent the midnight lockout that always seems to land before a morning meeting. If your home sits close to the coast, tighten the schedule to every nine months. Salt takes its toll.
Pay attention to patterns. If you notice a furnace that starts and stops several times before blowing warm air, mention it during service. Intermittent misfires often show up as longer preheat times, strange clicks, or exhaust fan cycling.
A few real-world examples from San Diego homes
In a Mission Valley condo with a closet furnace, the unit failed to light only after laundry day. The vent ran close to lint-prone areas, and the closet door weatherstripping starved combustion air. We adjusted the door venting, sealed the duct gaps properly, and cleaned the flame sensor. No more post-laundry failures.
In a Carmel Valley home, a modulating furnace would throw random ignition faults during high wind advisories. The termination cap faced prevailing winds, creating pressure pulses. We switched to a concentric vent with a different cap and shortened the exposed section. The ignition stabilized even on blustery nights.
In a Point Loma bungalow, an older furnace kept cracking igniters every few months. Temperature rise was 20 degrees above spec due to a choked return. The igniter sat near the hottest section and suffered. We corrected duct restrictions, balanced registers, and the new igniter lasted years.
These aren’t outliers. They illustrate that ignition is a system, and the fix often lies a step away from the obvious part.
What to expect when you call for hvac repair San Diego
A reputable hvac contractor San Diego residents use regularly will start with your description of symptoms, check the last service date, and ask about any code flashes you observed. On site, they’ll verify the call for heat, observe the sequence, and take targeted measurements. Look for a clear explanation, a written estimate before parts are swapped, and an option for a maintenance plan if that fits your needs.
If your furnace is under manufacturer warranty, labor coverage varies, but parts are often covered for five to ten years when registered. A licensed hvac company San Diego customers trust will handle the paperwork and source the exact part, not a near-match that could create new issues.
Response times in peak season can stretch, so keep that in mind when you schedule. If heat is critical due to health concerns or small children, mention it. Many companies reserve emergency slots each day.
The bottom line on getting ignition problems fixed
A furnace that won’t light is frustrating, but the root cause is usually straightforward once someone follows the sequence and measures what matters. Start with safe homeowner checks. When that doesn’t do it, bring in trusted hvac contractors who will test, not guess. Our climate adds some quirks, especially with vents and salt, but the fixes are reliable.
If you’re scanning for an hvac company near me because your house is cooling down, prioritize licensed, local teams with a track record of solving ignition faults, not just resetting boards. Ask how they verify flame signal, pressure switch operation, and gas pressure. Those three checks resolve most calls.
A furnace is a quiet partner in your home’s comfort. Keep its ignition system clean, verified, and protected from the elements, and it will light on command when that damp evening breeze slips under the door. And if it doesn’t, San Diego has the expertise to get you warm again without guesswork.